Just installed the Fluidmaster 400ARHRK (http://www.fluidmaster.com/our-products/toilet-fill-valves-toilet-parts/400arhrkp10-performaxr-all-in-one-toilet-repair-kit.html) and we still have a slow leak of about 1/2" in the tank. Can't figure it out. The water in the tank drops about 1/2" maybe every hour or so. The tank refills to the proper level. Then it will drop again 1/2". Repeat.

You can see the discrepancy in the water level in the photo below, the tank has lost water about 1/2".

When I shut off the water supply to the tank the tank looses more water but doesn't empty.

There are no leaks onto the floor, on the outside of the tank or anything like that.

There is plenty of slack in the the flapper chain. Flapper fits snugly. The kit came with a new rubber gasket as well.

I saw this on another forum, which is what we are experiencing: "If it drains down to a certain point and stops, then you have the small refill tube stuck too far down into the overflow pipe." But in our case the refill tube sits above the overflow pipe - see photo below.

We don't see any pieces of the old flapper or any "debris" that could be stuck somewhere to cause the tank to lose water. We are thinking of disassembling and starting over but can't see that helping.

Any ideas??

enter image description here

Not sure if this makes any difference, I turned off the water supply from the house to the tank this morning and at lunch the tank is totally dry. Does this help me at all?

So I know the water is leaking into the bowl and not the floor/outside the tank.

Should I still do the dye test? Will that pinpoint where the leak is occurring (flapper, overflow pipe, seal beneath flapper)? Or does the dye test just show you it's leaking into the bowl (which I already know)?

They sell a seal of sorts I see that you put on top of the thing that the flapper lid (I think) closes down on that is supposed to maybe help flapper leaks. Should I get this?

I just know if I will be able to determine from where the leak is occurring...?

  • Just to make sure... You took the tank off of the bowl, and installed every single part that kit comes with?
    – JPhi1618
    Commented Nov 13, 2015 at 14:03
  • Yes. We did all that.
    – Amanda
    Commented Nov 13, 2015 at 14:05
  • can you hear any leaking? Does it appear to be leaking into the toilet bowl (for instance, it flushes itself eventually)?
    – rogerdpack
    Commented Nov 13, 2015 at 14:16
  • 1
    I don't hear any leaking. I am not aware that it "flushes itself," ever. 1/2" water gets lost, then the tank refills. And water will come out of refill tube into overflow pipe/flush valve. The tank water level is correct again. Until it looses 1/2" water. Then it repeats. If it leaks into the toilet bowl it's very slow - but I guess that's where the water is going since it's not on the floor...?
    – Amanda
    Commented Nov 13, 2015 at 14:21
  • 2
    Put a few drops of food coloring in the tank water, then wait. See if the bowl water changes color. Then make sure the flapper is seated properly.
    – Tester101
    Commented Nov 13, 2015 at 14:48

1 Answer 1


If your tank is constantly leaking water, but you've not found it anywhere, then it is nigh on certain that it's going into the toilet bowl. Tester101's tip of putting food colouring into the tank and seeing if it appears in the bowl will likely confirm this.

The issue is then to find exactly where the leak is. Either your flapper isn't closing properly, there's a leaky joint where the overflow pipe connects (just below the flapper), or the seal between the flapper apparatus and the tank isn't watertight.

I would hazard a guess at it being the seal between the flapper apparatus and the tank, probably due to either under-tightening or over-tightening when installing the new flush. Over-tightening is perhaps the more likely - it shouldn't be tightened too much or you will distort the rubber seal.

  • OK, we will check the seal "tightness," I think that's one thing we haven't readjusted. TY
    – Amanda
    Commented Nov 13, 2015 at 15:00
  • +1 for mentioning the over tightening, it is fairly common for the flush valve seat to become warped due to age and/or over tightening if the large hex nut, preventing a good seal even with a brand new flapper. Commented Nov 13, 2015 at 15:29

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