Flushing out the answer

Here at Status-Q headquarters, we’re having a new bathroom fitted, which means we’re getting all these newfangled gadgets that you youngsters just take for granted. Things like mixer taps, which our international friends are amused that we didn’t adopt about 50 years ago. I tell them that British plumbing is like the weather: it’s unpredictable, and we like it that way, because it gives us something to make polite conversation about when inspiration is otherwise lacking.

Anyway, we now have a cistern with one of these dashed clever dual-flush buttons. You know, with a small difficult-to-press button embedded in a large crescent. I think it’s a kind of Islamic yin/yang symbol. But the real mystery is that nobody seems to know quite how it works. It didn’t come with a manual, and even our plumber couldn’t answer some of my questions. Here are a few – perhaps the readers of Status-Q have greater lavatorial expertise than we do:

  • It appears from visual inspection that the small button provides a smaller flush than the big one (these things are difficult to measure, but that seems sensible). But what happens if you press both, which is the easiest thing for my chunky fingers? Are they additive in some way, producing a megaflush? Or is that the same as the big button alone?
  • If the authorities really want us to save water, shouldn’t the big easy-to-press button be the one that does the smaller flush, leaving you to add on the side button for the full monty?
  • In any of the above combinations, does a press-and-hold give you any more than a brief press?
  • Is there an international standard for flush-button-operation, or might all of the above vary by manufacturer?
  • How many unnecessary gallons of water are used around the world each day by people like me who, in the absence of such vital information, always press the biggest combination of buttons for the longest amount of time? Can Status-Q make a significant impact on world water consumption?

All enlightenment most welcome! Or failing that, I’ve at least given you something to ponder next time you’re sitting there…

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Or we’ll just wait for Status Q Laboratories to do the experimental work and report back their findings on arxiv.org? 🙂

I have a pair of these toilets at home. The larger button releases the all of the water in the tank, just as a single flush toilet would, by opening a drain at the bottom of the tank. The smaller button opens a drain a few centimeters above the bottom of the tank, releasing most of the water in the tank, but leaving behind the water below the drain opening.
– Thus, pressing the two buttons together is the same as pressing just the big one.
– Holding the button down is unlikely to have much effect, but, shortly after the water the tank is released, a floating sensor falls with the water, allowing more water into the tank from the pipes in the wall. If you continue to hold the button down, the drain stays open, so the bowl receives the tank full of water, plus the water that would otherwise refill the tank (of course, if your usual button press is short enough, you might not get the entire tank, but this is unlikely).
– Toilet innards aren’t standardized, but I’ve only seen one basic approach (and I’ve worked on at least a dozen toilets).

To make it easier to hit the small button, you can start by removing the lid of your toilet. You should see that the metal buttons are designed to rest upon two buttons in the tank that control the two drains. If you put something (preferably adhesive and water resistant) on top of the small flush button in the tank, the metal button will be raised when you put the lid back on, thus making it easier to hit.

P.S. I’ve done my best to avoid using American terms that don’t translate, but please let me know if I can clarify any of this.

Thanks David, for an excellent explanation!

“If the authorities really want us to save water, shouldn’t the big easy-to-press button be the one that does the smaller flush, leaving you to add on the side button for the full monty?”

I’ve been pointing this out for years. Seems much more sensible.

I’m glad it’s not just me that’s wondered these things. I had all the same questions as you and anyone I’ve asked just shrugs and says, just press all the buttons and it’ll definitely work – entirely defeating the water saving purpose.

Further to David’s point upthread, I’ve recently installed a pair of (extreme budget) toilets, and on those, the buttons you press communicate with the actual-flush-buttons inside the cistern by plastic beams, which had to be cut to size as part of the installation process. It’d be very easy to cut a few mm off the plastic beam of the big-flush button so that the small-flush button sticks up higher. (And I plan to make just this modification tonight!)

The two-button option seems a newer innovation than the press-and-hold-for-full-deluge style, but I have encountered at least one model of toilet that has both facilities. Perhaps not coincidentally, it appears highly prone to malfunction.

There are at least two different flushing mechanisms.
There are dual flush cisterns that use a tradistional looking lever or chain. They rely upon creating a syphon which breaks at different levels. Personally I rather like this method as they are inherently more reliable than valve mechanisms since they cannot leak into the pan when the valve wears out. In fact the old UK water bylaws dictated valves could not be used and so siphons were the norm (I think I’m correct in saying this but maybe there are plumbers out there who know more).

The push button dual flush that you have uses a different mechanism – the drop valve. This has an adjustable float that controls the volume of water for the small flush. The big flush is usually 4 to 6 litres, while the small flush is 2 to 3 litres. Just watch out that the valve does not leak – can be a problem in our hard water area as limescale builds up.

I’ve seen two different methods for actuating also. Where the buttons are on the lid of the cistern they actuate each mechanism indepenently. Cable actuators for concealed cisterns are a little more clever. They use a single control cable, a short movement invokes the little flush, a larger movement triggers a big flush.

The question in my mind is how many leaky dual flush drop valves does it take to negate the water saving benefits of converting from syphon to valve mechanisms.

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