I went into my extra bathroom today and noticed both sinks were filled to the brim with water, no overflow. Both of these sinks share a drain in the middle and I’ve had a clog before but couldn’t snake it because it just went from one sink to the other and wouldn’t go through the middle pipe that drains out.

I did just have a new HVAC system put in this and it is in the attic above this bathroom. Not sure if that has anything to do with it. Also, flushed the toilet the other day and heard a glug type noise but it seemed to go back to normal.

Any ideas what could cause this? Could it be the HVAC or is that just coincidence? I assume there’s a clog somewhere down the line but I can say for almost complete certainty that nothing has been put down those sink drains.

  • The HVAC system should have a condensate drain. See where that goes... Jul 21, 2023 at 1:28
  • @manassehkatz-Moving2Codidact not going to lie, I went up there but it’s really tight in my attic and I couldn’t really tell what I was looking at. The only drain on that side of the house is this bathroom though (unless it has its own drain, which I wouldn’t imagine is usual), it’s almost above the bathroom. Jul 21, 2023 at 1:47
  • So it sounds like (but really just guessing here) you (a) either have a clog or a serious venting problem and (b) condensate drains into the same pipe so it backed up into the sinks. On a hot humid day you can get a LOT of condensate - basically squeezing the water out of the air. Jul 21, 2023 at 1:58
  • @manassehkatz-Moving2Codidact went back up and it’s definitely draining to that drain. Nothing in the overflow pan though. The pipe is definitely clogged, if it was the AC or not I’m not sure anyone can say. I’ll call the AC company in the morning and if they punt I’ll call a plumber. You have to snake it from the roof anyway so I can’t do it. Jul 21, 2023 at 2:13
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    Nothing in the overflow pan because the clog isn't right at the HVAC (sometimes it is, or more often it has to drain up using a pump, and the pump fails - but you're in the attic so it drains down), it is farther down so it gets down past the sinks and then hits the clog and comes out at the lowest point above the clog - which is your sinks. (Sometimes it is toilet or tub/shower, depends on how your pipes are set up.) This is going to be a plumber job unless you can take apart the drain pipes below the sinks and snake from there. Jul 21, 2023 at 2:22

2 Answers 2


Just wanted to update this with an answer. Needed a plumber to come out and clear the pipe. Where the T is where the two sinks meet was clogged, since it is an old style you go from one sink to the other when trying to snake it so you have to go in from the roof.

The reason it became an issue after the new AC unit is because the new unit was pulling a lot more condensation and so it backed up faster. The clog wasn't 100% so some water could slowly drain out. Given those sinks don't see a ton of use, any time it was used there was enough time between the next use so it just never built up until the new AC unit was installed.

Plumber suggested a cup of drain-o type clog remover every three months as a preventative. Need to change out that T to a newer style that you can snake easier and save me the plumber bill but with the pipes behind the walls you can't tell where they meet and it's no guarantee that it is in the middle. He has a camera he can use that would tell so I wouldn't have to go tearing up my walls hoping for the best, might do that and put in an access door so I can clean it out easily.


It looks like the AC condensate drain is sharing a section of plumbing, and that there is an issue.

Usually, it's easy to disassemble the drain under a sink (with a bucket underneath!), remove the p-trap, and then snake through the common drain pipe. Also check the roof stack vent, which can cause backup, as well as odors.

[BTW, I recently had an acquaintance tell me of ceiling and wall damage due to condensate overflow from a newly-installed split AC.]

  • The problem is I have two sinks and if you try to snake it, it just goes into the other sink. Last time I had a clog the plumber got it from the roof so I guess I’ll have to do that again Jul 21, 2023 at 2:14
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    You need to fix your sink drain problem, it was improperly constructed. You need a cleanout that can actually access the sink drains, all the way into the wall and down.
    – kreemoweet
    Jul 21, 2023 at 2:25
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    @user1723699 As the answer states, you take off the trap and snake directly into the drain pipe, not through a sink, in the situation you have described. Put some pictures in by editing your question and we can give more detailed advice.
    – Ecnerwal
    Jul 21, 2023 at 2:40
  • @kreemoweet I agree but it is not accessible without ripping apart a wall. I am heavily considering it now as it’s the second time I’ve had this issue. Jul 21, 2023 at 10:10
  • @Ecnerwal if it didn’t mean ripping out drywall to (hopefully) be able to access that I would. There is no current access to the middle drain pipe. Jul 21, 2023 at 10:11

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