I can’t figure out what this hole is for. The toilet has a plastic insert in the tank to reduce flushing volume. The circled hole is a plastic tube that goes up to e top of the tank and sits inside the plastic insert.

The toilet is a ProFlo 3612 The insert says “fluidmaster”

The seal between the plastic insert and the main tank (black thing in the second image) is failing, so I want to remove or replace the insert.

Photo of Tank

Tank inside

In the bottom of this photo you can see the tank insert.

1 Answer 1


It's presumably the same function as the similar tube on a standard old-fangled flapper valve toilet - overflow and bowl filling.

Overflow if water level gets too high. Say if the fill valve fails or is misadjusted - water goes into the bowl, not out the top and onto the floor.

Bowl-refill by having a small jet from the fill valve directed into it as the tank fills. This brings the bowl level up from where it is if you flush without the water turned on.

Some old-fangled toilets keep it down to one big hole by building the overflow tube into the flapper valve seat, so the outlet is below the flapper but sharing the same big hole.

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