So, earlier this week my better half shows me the sink in the guest bath (which she uses as her primary) was draining very slow. Okay, I'll take it apart this weekend. While I was at work (without telling me it was planned) she used the wet vac to dislodge whatever was stopping it up. Didn't get anything but water. But now the drain is well and truly plugged. Used my hand siphon pump and pumped the water, disassembled the trap, and ran my small hand snake as far as I could. Can't get it past the second elbow as my snake isn't very good. Don't want to force it and risk any damage to the pipes. I did get one hair mass out of it. Didn't find any insulation in the drip pan drain line (it drains into this sink trap) and no water in it. Reassembled and ran some water. Drain still plugged. Okay, this is beyond my capabilities and tools. Time to call a plumber. But we have another bathroom so it's not an emergency.

But here's what's driving me nuts. Later that night the sink is full. This despite not being used. I pump out the water. I even go and shut off the water so we can't even use it by mistake. Few hours later, more water in the sink. It's backing up from somewhere. But can't figure out how. Not backing up in the toilet or the tub in that bathroom. The toilet still works. The tub still drains fine. None of the other drains in the house are backing up. I'm trying to wrap my head around what's going on here. Any ideas?

EDIT: The more I think about it, it's most likely the condensate from the AC. It's the primary drain from the evap (pan drains outside).

You're going to have to isolate which drain is making that particular sink back up.
I'd drain the sink like you're doing now and then run individual water sources(toilets, sinks, etc.) until you find out which one is backing it up. Go from there.
Could be as easy as some drain opener or the need for a professional plumber.
Good luck.

I hate plumbing but have done a lot of it as a homeowner of various houses over 50 years. Sounds like you have a clog downstream from your sink and your drain line is shared by another drain upstream. I have had good luck over the years clearing clogs using a balloon-type drain opener. Drain King makes one. It attaches to the end of a garden hose and after you insert it into the drain line and turn on the water, it swells up and seals the line while sending a pressurized jet of water downstream. Be patient and let it run for a while. If it is a hair clog it will come free. I have not yet met a clogged sink drain that it won't clear. You also probably have a drain cleanout plug for the main waste line somewhere outside

Be careful with a "Drain King" type unit hooked to your hose. It will force water up the vent if the drain is plugged (which it is) and come out the pipe when you shut off the water making a huge mess.
Hair is generally the problem when you have a clogged bath lav (that your wife has been using)
It needs snaked. The water is coming from another drain tied into that lav drain OR as you stated a condensate drain.
Is the other bath sink on the backside of the plugged sinks wall? Lots of times they will run them into the same drain. It can be determined easily by sucking out the water in the plugged sink and running water in the other sink right away and check for water.
If it does not come into the plugged sink it is more than likely your condensate drain.
It needs snaked!

quote:

I have had good luck over the years clearing clogs using a balloon-type drain opener. Drain King makes one. It attaches to the end of a garden hose and after you insert it into the drain line and turn on the water, it swells up and seals the line while sending a pressurized jet of water downstream. Be patient and let it run for a while. If it is a hair clog it will come free. I have not yet met a clogged sink drain that it won't clear.

Everything I see on those say to push it into contact with the clog. Not sure I can. Can't even get a snake to it.

I’m not a fan of draino type chemicals, but I bought a gallon of stuff from Home Depot and used it in my old house in Washington. One and done. Safe for my pipes and the clog was completely gone. This crap did a great job dissolving whatever was in the pipe.

https://www.homedepot.com/p/In...eaner-1801/100126446

ETA: the sink was 99% stopped up. If I would let it sit for hours, it would drain fine for thirty seconds while the pipe filled, then back up.

I let it sit for about six hours so it was “empty”. Poured the whole gallon in. It filled the pipe and part of the sink. I left for work around 2 pm. Came home about 2 am and my problem was solved. Line was super clean and drained fine for the following two years we were in the house.

I had a bathroom sink drain problem recently and bought a small plunger (not the one with a pump) that's made for sinks on Amazon.
Worked wonders. With water in the pipe it doesn't matter how far down the clog is since this is a hydraulic method.

Go up on the roof and snake the vent near that bathroom. The clog is in the line just inside the wall and downstream from the sink, which is why the water from the A/C dripping into that line is backing up into the sink.

^^^^^^^^^^^^^^^
Correct answer

I have yet to encounter a clogged drain that couldn't be cleared with this stuff. It's cheap and easy to use. Empty trap, fill trap with this stuff. Rinse with hot water. It may discolor metal sink drain depending on finish/material.

Any type of plunger or water blaster that relies on built up pressure will not work because you
Have another drain line tied in before the clog as demonstrated by the drain backing up into the sink.

Your only options are going to be chemical or a snake.

I would try a good Draino type clog remover first because it’s easy. If that doesn’t work then run a snake down the vent as MikeinNC said or find the clean out and try to snake it out from there.

I have a bathroom sink that for years would get clogged about 12' down the drain line. Usually, I'd be able to snake it, but sometimes that just seemed to make the clog worse (perhaps by compacting the clogged matter). Besides, that's long way to work a snake down a twisty drain, chucking it into my 1/2" drill didn't help much.

I acquired a Drain King and suffered the predictable mess of sewer water backup onto my bathroom floor. Then I had a semi-brilliant idea, and cobbled together a hookup of the Drain King to my air compressor. Remove the trap and connecting pipes under the sink down to the nipple coming out of the wall, insert the Drain King and turn on the air. You will hear a steady stream of air flow out the vent pipe. Climb up on the roof, and cap the vent pipe with your hand, and/or a rag. You will feel air pressure build, then a sudden release, this is the clog being pushed down the sewer pipe. Much more sanitary than pressurizing with water. Do NOT try to pressurize from the vent, there will be major cleanup required. I should also mention that this approach requires a fairly straightforward connection between the clogged pipe and it's associated vent, too many branch drains or vents will defeat its effectiveness.

I'd be happy to provide a description of this unit if anyone is interested., it is just a couple of pieces of hose, some fittings, and a valve.

These days I try to stay on top of things and clean the trap, and easy-to-access drain pipes as soon as things start running slow, this keeps the clog/debris from migrating downstream to where it becomes a real problem. Pretty much within a day or two after my wife colors her hair.

HayesGreener-thanks for the heads up on this!

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