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I noticed there is an extra T pipe under my vanity for cold water. It goes to basement and it looks like there is a hole in it as well. I cannot understand what does it do? It looks like there is constant water that goes inside it (I can see it from the small hole it has).

enter image description here

The strange T part in close look: enter image description here

Arashsoft
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  • Looks more like some type of valve than a plain t-joint. Something to regulate pressure(?). – crip659 Oct 28 '21 at 17:57
  • You can actually _see_ water through that little gap in the nut? Can you stick a small screwdriver in there and pull it out wet? Is there water there _all_ the time or just when using the sink? – FreeMan Oct 28 '21 at 18:16
  • @FreeMan there is water all the time, I noticed that it is causing minor leak recently. Maybe it is damaged and there should be water only sometimes? – Arashsoft Oct 28 '21 at 20:04
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    Does the pipe going to the basement go to something like a floor drain that would usually not have water flowing to it (if not for the water that this source provides)? – Greg Hill Oct 28 '21 at 20:07
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    Trap filler is indeed a good bet, @GregHill – Ecnerwal Oct 28 '21 at 20:15
  • I searched about trap filter and I think that is it. I followed the line in basement and it goes to drain. – Arashsoft Oct 28 '21 at 20:51

1 Answers1

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It's a trap primer. It allows just a little bit of water to be bypassed from the usual horizontal path (headed to your sink) and sends it out the vertical pipe, where it ends up keeping a trap (often in a floor drain) from drying out and allowing sewer gas into your house.

Here's a photo of one from a vendor. https://www.sustainablesupply.com/products/zurn-trap-primer-bronze-pipe-dia-1-2-in-z1022-xl-1-2-ip-c1912466

trap primer

And another one (from https://www.wilmar.com/Sku/15-1843/mifab-continuous-flow-trap-seal-primer-with-12-in-connections-779897963421-mi-tsp-1) that looks even more like the one in your photo:

trap primer

(Thanks to Greg Hill and Ecnerwal for pointing me in the right direction with their comments.)

Doug Deden
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