Well I'm at my wits end. The toilet's been running for weeks and I've yet to catch it.

I first replaced the flapper, it still leaked. Then I replaced the flush assembly, it still leaks.

Now at this point I experimented a bit, and I filled the tank half way before turning off the water. It stayed steady for 2 days. But when allowed to fill properly, the tank completely empties over the course of 6 hours.

Could it be possible that the tank itself is somehow to blame? Could it be that I didn't tighten the tank down enough?

2 Answers 2


The issue was indeed a siphon, and it was actually a very silly cause.

Upon removing the fill tube, I noticed the water level on there was at the same level as the water level in the tank. But hold on a second, why would one see a water level on the fill tube?

Well it turns out that at some point, the clip that goes on top of the overflow pipe which is supposed to hold the fill tube was lost. The tube for the past few years was just tucked into the overflow pipe slightly. There must have been a disturbance in the force or the tube somehow pushed itself down after all these years, but once the tube was below the water level, it did indeed siphon water out of the tank through the fill valve and on into the bowl.

I feel like this should have been the easiest thing to catch, but for future reference, the solution is to use the fill tube clip.


All I can think of is you are developing a siphon between the tank and the bowl. How high does the water get to the top of the overflow? The overflow pipe is the one that sticks up in the tank.

I would try to set the float level (what ever kind of float it has) such that the water in the tank is an inch below the top of the overflow pipe and see what happens.

  • I have the float set to just about the bottom of its adjustment span (less water, eco-friendly!) and the overflow is cut about an inch below the flush handle. The float cuts off about 3 inches below the overflow - the water is now going through the overflow
    – kavisiegel
    Feb 28, 2015 at 13:28

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