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I am in the middle of a bathroom reno, and want to relocate one of the 2 sinks. Right now the sinks are on different walls 90 degrees from each other, and I like to relocate one so they are on the same wall. My question is, can I use the waste/vent from the sink that is already on that wall for both sinks, so I can avoid running drain PVC all the way around the 90 degree angle to its current waste/vent? If so I'd just cap the unused waste/vent pipe and call it a day.

I am obviously an amateur, and this is my first real DIY reno, in a home we just bought.

TIA

  • Probably. Specifics will depend on the size of the current pipe for the pipe you want to "double up" on, and how close the two sinks will be (which mostly affects whether you need a new section of vent from the second sink to the vent you want to double up on, or not.) Can you add those details? The key phrase for self-research on drain capacity is "fixture units." – Ecnerwal May 6 at 2:27
  • The waste is 3" and vent is 2" – CGAFT May 6 at 19:59
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Yes, you can use the same vent.

If you have the wall opened up, consider how you can improve the venting. A lot of houses have sucky venting.

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Yes use one for both the waste and vent. If the existing sink doesn't have issues draining, your vent will be fine. For the waste, just "T" the two sinks together and join them to the existing drain/waste pipe. Do the same for the water supply for the sink. Remove the existing cut-off valves and put a tee on the stubbed out pipe with the opposite end of the tee pointing at you and the leg of the tee pointed to the new sink. Run a new piece of pipe from the tee over to your new sink and put a 90 on the end. Connect your shut-offs for the old sink at the tee and for the new sink at the 90. Of course you'll have to run a hot and cold line. You don't have to, but I would replace the existing cut-offs with new ones while they are off. Good luck!

Normally you would stub out a drain for each sink and then have a p-trap directly under each. This is what is shown in the photo , before the p-traps are installed. It is permissible to have one trap, but if you do, it has to go below the tee. I'm old school and don't use Shark fittings. I'm not sure if they are acceptable in a sealed wall or not. Hopefully someone else can help you there. DualVanityRoughIn

  • My plan is to add an aditional T above the existing one on the waste/vent pipe then run pvc through the studs to the new sinks location, so each sink can have a trap, and I'm not dealing with excess plumbing under the vanity. Will having the Ts stacked on the waste/vent cause any back flow issues to the one on the bottom? Also, my house has pex water lines so I plan on extending the line using shark bites through the studs (holes were already drilled) to the new location. Can anyone see any deficiencies in this plan, or recommend an easier way to go about it? Thank you all very much – CGAFT May 6 at 20:00
  • It took me a minute to catch on! You can stack 2 tees, but the best way is to use a "cross" fitting. If you stack 2 tees, the new drain line will have to be higher than the existing one, because you have to slope the line towards to drain. It could even be too high for a trap to fit. – Mark May 6 at 22:10
  • I greatly appreciate the help, one more question for you. Is it going to cause an issue if I just T into the water supply of the sink that was already on the wall, instead of running new pex from the previous location? I would like to leave the old supply lines in place, so a tub could be added easily in that location in the future, but do not want to cause water preasure issues by supplying 2 sinks with one supply source. Thanks again. – CGAFT May 7 at 3:59
  • It will cause no problem whatsoever.That is what I would do rather than running the old water line around the corner. – Mark May 7 at 14:05

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