[EDIT 2016-09-28: It is a Kohler toilet, and the old fill valve is Kohler 81093-AA. I suspect it is the original valve. I've been in correspondence with Kohler. They asked for pictures of the toilet to identify it, which I sent. They didn't respond to my question about cutting the existing overflow-pipe. They gave model number 1138930 as an appropriate replacement, however they said it may not extend as far as I needed, so extend it all the way and should be ok. That was voicemail, so I emailed back asking for the height-range of the 1138930. Waiting for the reply.]

[EDIT 2016-09-28: still waiting for a reply to my follow-up email (but installed the 400ARHR and the project is done.]

Kohler toilet with original Kohler guts runs. It is old and is not a low-flow toilet.

Lifting the float by hand does not stop water flowing out the bowl-refill tube attached to the overflow pipe. So I bought a new valve.

New valve is the Fluidmaster 400A. It's height is adjustable, but it doesn't extend quite long enough for the Critical Line on it to be 1" above the top of the existing overflow pipe. The manufacturer did not stamp a water level mark inside the tank, though there is the water stain.

Is it ok to cut off about an inch of the overflow pipe? might need to cut 1.25 or 1.5. Haven't measured precisely.

2 Answers 2


Not only is it ok, but Fluidmaster gives instructions on where and when to cut the overflow tube, as the follow photo shows.

enter image description here

Fluidmasters Article states the following:

The most important part inside the tank is the flush valves "overflow pipe." The overflow pipe is the safety net for your toilet. When properly set it will prevent water from overflowing the tank and flooding into the home.

The four critical areas of a toilet tank are:

  1. The Tank Lever Hole
  2. The CL (Critical Level) Mark located on Fluidmaster's fill valve
  3. The Overflow Pipe (top end)
  4. The Water Level

The water level should be indicated by a mark or (depending of the age or use of the toilet) a water stain on the inside of the tank. When rebuilding a toilet it is very important to set the fill valve to achieve this height.

  • ...it is very important to set the fill valve to achieve this height. That is the crux. There is no mark, but there is a water stain. Trimming an inch off the overflow tube, will lower the water level by an inch, and thus an inch below the stain level. With the new valve and the old overflow tube, it is not possible to have both the old water level and a 1" CL clearance.
    – Arlo
    Sep 27, 2016 at 7:10

Via online chat, Fluidmaster told me that model 400ARHR extends 10-15", which is 1" more than 400A 9-14". Returned the 400A and bought the 400ARHR, which my local store carried as well. So there was no need to cut the top inch off the overflow pipe. However, now that I understand a bit more, my tank is a multi-flush tank. A regular flush drains the tank by about 2", as regulated by the float level on the flapper chain. leaving about 10" of water in the tank. So it may have made no difference to trim the overflow pipe by an inch or two in order to accommodate the 400A per code.

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