Anyone know what this is for

This is a bathroom in an office building. The grey pipe appears to be PB, but what is it used for???



Might be a trap primer for a floor drain.

I found one like this traced it to the TPR valve discharge .
Great if it goes of when some one is washing .
A definite Hazard immediate repair or replace.

Roy Cooke


It is not for the water heater. The heater drains to the outside of the building. There is also one in the other bathroom.


You might be on to something.

When I first looked at it, it did put me in mind of a dishwasher type tailpiece, except that the branch is tipped the opposite way on your picture. That’s what made me think that maybe it was for a trap primer.

I just Google’d “trap primer tailpiece” under images, and this is the picture that came up. It appears identical to yours:

Another trap primer tailpiece:

trap primer tailpiece.jpg

It’s not a trap primer like I’ve ever seen. Without seen where it terminates I can only guess and I don’t have a good guess.

Trap primers come in many varieties. The goal is to get a trickle of water in the floor drain every once in a while. They have trap primers adaptors for Sloan valves on toilets and urinals. They have trap primer kits for laundry tub and mop sink faucets, where the faucet has a little 1/4" tapping. They have trap primers that work sorta like a PRV in reverse that go in the city water feed. They have trap primer sink tailpieces that divert a little splash of the handwashing water down the trap prime pipe. They have trap primer kits that go on freestandind drinking fountains. These are the one’s that are known to me, and I’m betting there’s many more styles.

Did you check the source for water to the office coffee maker?:lol: