Down the Drain
October 4, 2020 3:46 PM   Subscribe

According to Thames Water, dual-flush toilets specially designed to save water are wasting more than they conserve, thanks to leaking.
“The majority of [dual-flush toilets] use the drop valve system, which sits at the bottom of the cistern and opens to allow the water to flow out when the flush is pressed. Debris and other issues can cause the mechanism to fail to close, meaning water continually flows from the cistern and into the bowl.

“Older cisterns tend to use a siphon system, which works by pushing water upwards until it reaches a point at which it can flow into the bowl. Because that point is above the waterline when the toilet is not being flushed, the system is less likely to develop the same sort of leak.”
posted by adrianhon (63 comments total) 9 users marked this as a favorite
 
Older cisterns tend to use a siphon system, which works by pushing water upwards until it reaches a point at which it can flow into the bowl.

Um...are UK toilets different from American toilets? Because ours tend to have a flapper valve in the bottom of the tank, and yeah if it leaks you hear the water run to refill it. You replace the flapper every 5 years or so.
posted by Huffy Puffy at 3:55 PM on October 4, 2020 [4 favorites]


Yes, I believe UK toilets are different from US toilets. Part of the reason I posted this is because not a week earlier, I had this exact problem with our dual-flush toilet.
posted by adrianhon at 4:05 PM on October 4, 2020 [5 favorites]


Very different. Can't stand the N. American flapper valve system. Its only saving grace is that you can do a short flush: tap the handle while it's flushing, and it'll stop. Can't do that with a UK siphon system.

UK toilets have a little plunger the gets pulled upwards, pushing water over a siphon lip in the tank. This draws all the water in the tank down to the bowl. Once the tank is empty enough, the siphon breaks and the cistern starts to refill. Because the siphon is above the tank water level, it can't leak. But ones it starts to empty, a single-siphon toilet will flush the whole cistern.

Really old UK toilets used a bell-like siphon cover. They often didn't seal well enough to flush.
posted by scruss at 4:07 PM on October 4, 2020 [3 favorites]


5 years seems fairly pessimistic tbh, we have had ancient ones that still held water just fine.
posted by Ferreous at 4:07 PM on October 4, 2020 [1 favorite]


Tbh the bigger issue I find is that older or cheaper toilets in the US tend to be badly glazed in the trap so stuff goes through poorly and requires more water to do so. The difference between a cheap box store toilet and a proper one of even the same model at a plumbing supply place is noticable.
posted by Ferreous at 4:11 PM on October 4, 2020 [2 favorites]


Dual-flush siphons definitely are available. I'm surprised that push-button mechanisms fail so often. I've not seen this. I think my experience is about 50%-50% push button vs. siphon toilets. I do much prefer a siphon, personally.

I think I've found the originating press release for this article
Three separate studies have found that around 80% of leaking toilets had a flush valve[PDF] mechanism rather than a siphon. As well as the 80% reported in the Phase II study Anglian Water also found 78% of 326 leaking toilets in Newmarket had a push button mechanism. Thames Water has found 80-90% of leaking toilets have a dual flush mechanism.
posted by ambrosen at 4:13 PM on October 4, 2020 [1 favorite]


The BEST kind of toilet is the compost toilet. They waste the least water and are now permissible under international code even in major cities. (Extra paperwork may apply.)
posted by aniola at 4:51 PM on October 4, 2020 [2 favorites]


I have found that the "use less" flush button is usually adequate for all flushes.
posted by aniola at 4:51 PM on October 4, 2020


I have done this before.

Vaseline on flapper valve.
posted by Splunge at 5:27 PM on October 4, 2020 [1 favorite]


Still better than the traditional German toilet
posted by Saxon Kane at 5:32 PM on October 4, 2020 [2 favorites]


I have done this before.

Vaseline on flapper valve.


Definitely a temporary solution. Petroleum jelly could deteriorate the flapper material and really make it fail. Silicone grease, which is sold with plumbing supplies, is a better substance to condition the rubbery parts in the toilet. Might be a good life extender on a replacement flapper. Seems to resist washing away like petroleum greases and doesn't attack rubber or plastic.
posted by 2N2222 at 5:58 PM on October 4, 2020 [5 favorites]


Metafilter: The difference between a cheap box store toilet and a proper one of even the same model at a plumbing supply place is noticable.
posted by transitional procedures at 6:03 PM on October 4, 2020 [3 favorites]


Just moved into a house (in America) with two of these toilets. What steps should I take to prevent leaks?
posted by mad bomber what bombs at midnight at 7:02 PM on October 4, 2020


Vaseline on a Flapper Valve is the name of my neo-swing band's latest album.
posted by Greg_Ace at 7:28 PM on October 4, 2020 [8 favorites]


What steps should I take to prevent leaks?

Don’t allow debris into your tank. :) Is top-decking common enough in the UK that “debris in the tank” is a serious problem?
posted by Mister Moofoo at 7:30 PM on October 4, 2020 [3 favorites]


Thames Water has found 80-90% of leaking toilets have a dual flush mechanism

This is not policy-forming without knowing what proportion of all toilets have a dual flush mechanism, eh?
posted by clew at 8:15 PM on October 4, 2020 [7 favorites]


Three separate studies have found that around 80% of leaking toilets had a flush valve[PDF] mechanism rather than a siphon

Are there other disadvantages that explain why the siphon mechanism isn't universal, then?

Or is this one of those cases where some countries have adopted advantageous practices or technologies that people in other countries are just completely unaware of or wrongly superstitious about? That kind of situation can be really frustrating or tragic, like in the case of socialized healthcare in the US. But I also have a weird kind of fondness for it in less serious cases. There's something kind of exciting about it, like coming across mysterious archeological remnants or holdovers from a past civilization where there wasn't instantaneous global communication and international travel was a rare and difficult thing that few people undertook (heh).
posted by trig at 12:18 AM on October 5, 2020 [2 favorites]


I imagine I will regret asking but is “top decking” what I think it is?
posted by dmt at 12:45 AM on October 5, 2020 [1 favorite]


Surely it means filling the attic cistern with unfiltered roof runoff?
posted by clew at 1:02 AM on October 5, 2020 [4 favorites]


You need to replace the rubber washers on flush valves after 20 years or so to stop them leaking. Coincidentally I did it recently to our toilet and learned all about it. By the time I have to do it again I will have probably forgotten how. Also, do you even need a dual flush? With a single flush you can just press it part way until you start to feel resistance and water starts running down (enough to turn pissed-in water from yellow to clear) and then release it before you trigger a complete flush. It's an analog mechanism FFS!
posted by L.P. Hatecraft at 1:40 AM on October 5, 2020


Ohh, L.P. Hatecraft, you're right, except I've been trained out of the shallow flush: I grew up in a house with bad plumbing and only the full flush would work -- anything less would put the system into a bad state.

What about those pull up / push down heavy duty flushers? I assume they don't have leakage problems, but I sometimes have a hard time pulling up with my foot. (Maybe there is a way to pull up with your hand without worrying about being poo-splashed?)
posted by batter_my_heart at 1:54 AM on October 5, 2020


Also, do you even need a dual flush? With a single flush you can just press it part way until you start to feel resistance and water starts running down (enough to turn pissed-in water from yellow to clear) and then release it before you trigger a complete flush. It's an analog mechanism FFS!

A siphon based toilet doesn't allow you to do that, meaning there absolutely is a point to dual flush systems. It's also a... hacky solution at best. And it doesn't solve the leaking issue! The leaking issue isn't a dual flush issue, it's a flapper valve issue. So siphon dual flush doesn't increase leakage risk over the UK status quo (single flush siphon) but going to single flush valve absolutely would.

The takeaway from the badly clickbait-titled article isn't "single flush good, dual flush bad", it's "siphon good, valve bad".
posted by Dysk at 1:57 AM on October 5, 2020


Um...are UK toilets different from American toilets? Because ours tend to have a flapper valve in the bottom of the tank, and yeah if it leaks you hear the water run to refill it. You replace the flapper every 5 years or so.

Two differences:

First, as discussed here, the way the water flow is controlled.

The second difference is in how the water+waste exits the bowl. American toilets have a siphonic bowl, when you trigger it by flooding the bowl with water above the siphon line, a siphon is formed which sucks all the bowl contents out. UK toilets are "washdown" where the flush physically pushes the waste out and through the trap.

The American design is cleaner for the bowl (because there's a wider water area in the bowl for waste to fall into) but the siphonic design means a narrower waste pipe which is prone to clogging. If you're not American, you might assume that references to clogging toilets are either crude jokes or a result of American gluttony but this is not so, that really does happen.

This is why American bathrooms often have plungers (not commonly seen elsewhere) but much less commonly have toilet brushes (essential with a washdown design).
posted by atrazine at 2:42 AM on October 5, 2020 [7 favorites]


I have found that the "use less" flush button is usually adequate for all flushes.

When I had mine apart for decorating I discovered not only was there nothing preventing the installer putting the button in the wrong way round so it did the wrong thing *, but it was adjusted such that a half flush was almost as much water as a full flush, so completely pointless.

It was brand new when I moved in so I presume it came out of the box like that.

(* speaking of which, should the big side be for "half flush" because it's used more often, or to indicate it's for the bigger flush?)
posted by grahamparks at 2:51 AM on October 5, 2020


dmt: Yeah, pretty much.

To be clear, I’ve never done such a thing, nor would I.
posted by Mister Moofoo at 4:26 AM on October 5, 2020


As a Brit I think it's important to point out that our privatised water companies, and Thames Water in particular, would like nothing more than to shift the public perception of responsibility for leakages onto the public and away from themselves.
posted by Cardinal Fang at 5:29 AM on October 5, 2020 [8 favorites]


American toilets have a siphonic bowl, when you trigger it by flooding the bowl with water above the siphon line, a siphon is formed which sucks all the bowl contents out. UK toilets are "washdown" where the flush physically pushes the waste out and through the trap.

The UK design is standard in Australia as well.

Then there's your German/Dutch "shelf" toilet, essentially a washdown design like the UK one but cunningly designed in such a way that all your turds remain sitting well above the waterline until you flush.

I am semi-convinced that the high quality of German mechanical engineering has been at least partly driven by the extreme performance historically required of exhaust fans in German bathrooms.
posted by flabdablet at 5:36 AM on October 5, 2020 [3 favorites]


This is why American bathrooms often have plungers (not commonly seen elsewhere)

Huh. You know, I'd wondered for years why I couldn't find a freaking toilet plunger over here and finally had to resort to ordering a proper one off of Amazon. the_more_you_know.gif
posted by Mr. Bad Example at 6:18 AM on October 5, 2020


our privatised water companies, and Thames Water in particular, would like nothing more than to shift the public perception of responsibility for leakages onto the public and away from themselves.

Thanks, Cardinal Fang: I knew there was a reason for this story becoming a thing.

Hand-wash toilets need to be better known to the world outside Japan, too.
posted by scruss at 7:01 AM on October 5, 2020 [1 favorite]


(* speaking of which, should the big side be for "half flush" because it's used more often, or to indicate it's for the bigger flush?)

Yes, good question! This was the subject of a furious dinner table debate the other day, with half of the table arguing that SIZE OF BUTTON = SIZE OF STUFF TO FLUSH (big button for "larger deposits" and the small button for "tinted waters"), while the other half argued for ergonomics, so SIZE OF BUTTON = WHAT HAPPENS MORE OFTEN (big button for the more common "tinted waters", small for "larger deposits").

It had never occured to me before this that it was a debate. I'm firmly in the former camp though: clearly pee is conceptually smaller than poop, no?
posted by Ten Cold Hot Dogs at 7:11 AM on October 5, 2020


Sure it's the former camp because our toilets push down the small button when you push down the large button but not vice versa. IE: Big Button, Big Flush; Little Button, Little Flush.
posted by Mitheral at 7:21 AM on October 5, 2020


As a Brit I think it's important to point out that our privatised water companies, and Thames Water in particular, would like nothing more than to shift the public perception of responsibility for leakages onto the public and away from themselves.

This is not included in all of their leakage statistics because those are calculated (modelled, really) based on two things:

1) district flow minimum. Over the course of months they will look at the absolutely minimum level flow in the district, that is assumed to be due to leaks. Domestic leakages are included in that.

2) meter differences. In areas like London where most areas are now metered, they can calculate the differences between district flow meters and the downstream water meters. This will not include domestic leakages.

A *lot* of leakages come from the supply pipe between the water main and the premises. These are owned by the property owner but the water companies are obliged to repair them for free.

Thames has historically been by far the worst leakage performers. They claim this is because it's more difficult to access underground assets in London but Ofwat hasn't really bought that. You can see comparative results here.

In any cases, water companies have an incentive to reduce average water use in their areas relative to the other companies and get rewarded or penalised for that which is why Thames publishes things like this.
posted by atrazine at 7:47 AM on October 5, 2020


The Pythagorean Siphon Inside Your Washing Machine - Steve Mould talks about the siphons, about 5 minutes in or so is the bizarre UK siphon / half-flush thing that's a mystery to us of the tank and flapper clan.
posted by zengargoyle at 8:12 AM on October 5, 2020 [3 favorites]


I wish to amend a previous statement on a different subject:

Every religion and every toilet is weird except your own.
posted by Huffy Puffy at 8:21 AM on October 5, 2020 [4 favorites]


Sure it's the former camp because our toilets push down the small button when you push down the large button but not vice versa. IE: Big Button, Big Flush; Little Button, Little Flush.

Fully agree, but it's worth noting that on many toilet designs, you can choose! You can often just take the button mechanism out, spin it 180 degrees, and put it back in.
posted by Dysk at 8:22 AM on October 5, 2020 [2 favorites]


I'm staying in a place in a sustainable development right now that has vacuum toilets (like in airplanes). They work great! Highly recommend. They are, of course, loud -- but somehow not as loud as the ones in airplanes (maybe it's the accoustics?) and the noise they make lasts only a second rather than the interminable racket regular toilets make.
posted by antinomia at 8:23 AM on October 5, 2020 [1 favorite]


"tinted waters"

tank and flapper clan


Lots of wonderfully poetic language in this thread!
posted by Greg_Ace at 9:07 AM on October 5, 2020 [1 favorite]


The wine-dark WC
posted by aws17576 at 9:47 AM on October 5, 2020 [10 favorites]


Rhabdomyolysis?
posted by flabdablet at 9:50 AM on October 5, 2020 [1 favorite]


At least incineration toilets don't leak. The old one I used to use made an alarming “whoomp!” followed by a puff of smoke out the flue a few seconds later. A real crap crematorium.
posted by scruss at 10:59 AM on October 5, 2020 [1 favorite]


Hand-wash toilets need to be better known to the world outside Japan, too.

I ordered one of these for my toilet here and it works pretty well. They're apparently considered old-fashioned in Japan now but I think they're a great idea that should be adopted everywhere. A side benefit is you'll know if you have a leak in your toilet valve because the "sink" will keep going.

Also, in places with electric water meters that are in direct communication with the water company the water company should have to notify you if your consumption indicates there's a leak somewhere (higher than normal/some multiple of average for say 2 days). Right now they don't care because you're paying for the wasted water but if it became their problem they would. I rented a place for a year and noticed a leak in the toilet and was able to fix it. Not sure how long it was going on for but the bill for that period was super high.
posted by any portmanteau in a storm at 1:26 PM on October 5, 2020


Dual-flush toilets ... typically put out four or six litres, with the smaller quantity meant for clearing urine.

*Oh*

So you're using a loo somewhere, and it's got the dual-flush arrangement, and all you've used is a couple of sheets of loo roll, so obviously you're supposed to use the half-flush button, right? And it doesn't work. Doesn't clear the paper. So you flush again, still no, so you use the full-flush button and by now you're feeling really ashamed and embarrassed, I mean, you've been in here for ages now, taking up a cubicle, and who needs to flush the loo THREE TIMES?

And this happens over and over, every time you use one of these loos, and eventually you give up on the half-flush altogether, and just feel guilty for wasting water and inadequate for being unable to master the knack of flushing the loo with a half-flush button.

And then, YEARS down the line, you read a comment in an article and suddenly you understand... the half-flush button is for the half of the population that doesn't always need to use paper. It's not for you at all. It was never for you. All that guilt? Completely misplaced.

Gah.
posted by ManyLeggedCreature at 1:38 PM on October 5, 2020 [4 favorites]


We have a low flow toilet that uses a tipping bucket mechanism... there is a bucket in the tank that fills with water, and when you push the handle it tips the bucket over. Weirdest design ever, but it works and can’t leak by design.
posted by fimbulvetr at 2:17 PM on October 5, 2020 [1 favorite]


I've just gone and taken the top off my bog, and found which was the half flush (left) and which the full flush (right) and swapped it so half flush is the bigger button.

My general antipathy to English water companies was sealed when I saw that the average price of domestic water in California is exactly the same as it is here ($1.50 / 100 cu ft vs. £3.50/m³), despite my water coming from fields less than a mile away and flowing downhill to me and then out to the treatment works also under a mile away. I feel cheated.
posted by ambrosen at 2:22 PM on October 5, 2020


My general antipathy to English water companies was sealed when I saw that the average price of domestic water in California is exactly the same as it is here ($1.50 / 100 cu ft vs. £3.50/m³), despite my water coming from fields less than a mile away and flowing downhill to me and then out to the treatment works also under a mile away. I feel cheated.

Compared to Dutch or German water it's a bargain! (Also most Americans pay for their sewerage service separately whereas it's included in water billing in the UK so it's hard to compare directly).
posted by atrazine at 4:24 PM on October 5, 2020


Compared to Dutch or German water it's a bargain!

Really depends where in Germany you live, with prices ranging from half a Euro cent a litre in Berlin (about €5/m³) to less than €1.50/m³ in Munich.*

*I couldn't quickly find a straight-from-the-horse's-mouth cite on this, but lots of secondary sources agreed on somewhere around 1.30, so here is one of them in English.
posted by Dysk at 4:43 PM on October 5, 2020


(I'm not sure if German water charges include sewerage though, so it may not be an apples-to-apples comparison!)
posted by Dysk at 4:44 PM on October 5, 2020


And then, YEARS down the line, you read a comment in an article and suddenly you understand... the half-flush button is for the half of the population that doesn't always need to use paper.

It's entirely possible that things are different in your neck of the woods, as prevailing toilet flush designs do vary significantly by region, but I find that virtually all toilets will take a handful of sheets of toilet paper on the smaller flush just fine (in the UK, and my experience is mostly of comparatively new - i.e. not pre-war - plumbing).
posted by Dysk at 4:53 PM on October 5, 2020


And then, YEARS down the line, you read a comment in an article and suddenly you understand... the half-flush button is for the half of the population that doesn't always need to use paper. It's not for you at all. It was never for you. All that guilt? Completely misplaced.

First gen dual flushes were less than awesome in this regard. Newer stuff is better though I'm sure there is still some sub-optimal equipment being produced. The dual flushes in my place have no problem handling even a dozen or so squares of paper on the low flush.
posted by Mitheral at 5:14 PM on October 5, 2020


Is California and Germany strictly by volume? Where I live (BC, Canada but water charges are municipal or even private providers) We get charged a connection/delivery fee (which theoretically pays for the distribution network), and then the water is metered on top of that by the cubic meter. Sewage charges are seperate and flat rate by square footage (sort of) and use.
posted by Mitheral at 5:18 PM on October 5, 2020


In the US as far as I know the tank is sorta assumed to also be emergency water supply in case of disaster. Clean drinkable water. The hand-wash toilet design would make that unsafe to drink.
posted by zengargoyle at 6:10 PM on October 5, 2020 [1 favorite]


While it's true that tank water is generally drinkable (at least places where the water is chlorinated) US/Canada toilet tank water is considered non-potable. That is why tanks all incorporate some sort of siphon break on the incoming supply instead of a simple float valve.
posted by Mitheral at 8:08 PM on October 5, 2020 [1 favorite]


fimbulvetr, couldn’t the control that keeps the bucket from overflowing fail?
posted by clew at 9:17 PM on October 5, 2020


Sure, that is possible. It is a very simple float arm valve, so not much to go wrong with it.
posted by fimbulvetr at 9:33 PM on October 5, 2020


Supply water valves are a common service item on toilets but it doesn't matter what kind of (water) toilet you have they are going to have a fill mechanism at least as complicated. It's been my experience that leaky toilets are 50/50 flush valve/fill valve failures but I imagine that varies wildly depending on local water quality and contaminates (EG: hard water is hard on fill valves and chlorine is hard on the rubber of flush valves). So the bucket style flush would eliminate 50% of leaky toilets.
posted by Mitheral at 10:37 PM on October 5, 2020


Except that siphons aren't prone to leaking, particularly - that was in fact the assertion at the root of this whole debacle, the claim that dual flush toilets were leakier, because of equating dual flush with valve and single flush with siphon (which is not necessarily true). So the bucket system would eliminate half of leaks in places where siphons aren't used already, and not achieve much over a siphon (except being bulkier).
posted by Dysk at 2:07 AM on October 6, 2020


Is California and Germany strictly by volume? Where I live (BC, Canada but water charges are municipal or even private providers) We get charged a connection/delivery fee (which theoretically pays for the distribution network), and then the water is metered on top of that by the cubic meter. Sewage charges are seperate and flat rate by square footage (sort of) and use.

I think it varies by location. UK is historically flat rate for both based on property value (since the marginal cost of water production was relatively low compared to infrastructure costs) but they've been moving everyone to metering + annual fee.
posted by atrazine at 2:17 AM on October 6, 2020


I am very happy to see English water companies specified by ambrosen. Scottish Water is nationalised and you get billed as part of your Council Tax. Still relatively expensive, especially given how much it rains here.

Don’t allow debris into your tank. :) Is top-decking common enough in the UK that “debris in the tank” is a serious problem?
The words of someone who has never lived in a hard water area.
posted by Vortisaur at 6:30 AM on October 6, 2020 [4 favorites]


For reference: The average English & Welsh bill is £397 of which £186 is water and £210 is sewerage.

It ranges from £300 in wet and wild NE Wales to £470 in the dry Southwest. Strangely the second highest average bill is for Welsh Water (a not for profit company) which covers most of Wales but this is probably because the topography means that you have to maintain many separate systems rather than a few big ones.

Scottish Water is £369 on average.
posted by atrazine at 7:20 AM on October 6, 2020 [1 favorite]


I guess an advantage of the bucket system is that you also don't get silent leaks like leaky flappers. You would know there was a problem as the water would just keep on running and not stop.
posted by fimbulvetr at 8:07 AM on October 6, 2020


When a flapper valve leaks, you get intermittent toilet-filling noises when the float level drops enough. This is usually enough to get your attention.

(Also, those California water costs seem low. We pay in the $2 range, plus about that much in sewer charges, from our municipal light/gas/water co. here in the Mid-South [we don’t get our water from the big river though]).
posted by Huffy Puffy at 8:12 AM on October 6, 2020


First gen dual flushes were less than awesome in this regard. Newer stuff is better though I'm sure there is still some sub-optimal equipment being produced

The amount of water produced for each flush is completely adjustable by the installer - or anyone who likes to interfere. On mine there's a float that forces the flap closed once the water was dropped below a certain level. You can slide the whole thing up and down to make it happen at whatever water level you wish, no tools required.

When a flapper valve leaks

You get a constant audible dripping all through the night.

Drip.

Drip.

Drip.
posted by grahamparks at 8:31 AM on October 6, 2020


I haven't had a flapper-valve toilet in years. Downstairs is the bucket flush, upstairs is a dual-flush retrofit I installed in an older flapper-style toilet 12 years ago. No more flapper, no more float arm fill valve, and no toilet leak problems since I installed it.
posted by fimbulvetr at 8:40 AM on October 6, 2020


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