On Saturday night, I noticed a sink in a bathroom we hardly use was filled with water and approaching the edge. The overflow drain was also filled up from what I could tell so seemed obvious we have a clog. Sure enough this is one that the A/C drains into so water filled up the sink and I guess I got lucky that I caught it in time (glad the Aggies had a night game!). Removed the water with a cup, but by Sunday night it was back to the same level. This is a second floor bathroom so of course it was keeping me up all night.



Clearly need to get the gunk out, but not sure if this is a DIY or if I should call a plumber/AC tech to make sure everything is properly taken care of. If it's DIY, any thoughts on where to start? I've read different ideas including using a shop vac, snaking it, and pouring bleach or vinegar down the A/C drain pipes.



Also any thoughts on if this is something totally different? What's confusing to me is the actual drain pan hardly has any water in it. I would think a backup would cause the drain pan to fill up.



I'm not sure if it's related but we also got a ton of rain on Saturday and Sunday in Houston. Presume the air that the A/C is working on is a lot more humid.

Fairly simple DIY. Take the p-trap apart and clean it out. I use an old toothbrush to clean it. You can unclip and remove the drain stopper, which will allow you to clean the drain pipe from the sink bowl down to the p-trap as well. Unclogging the sink drain is likely going to fix your problem, but while you are under there, it wouldn't hurt to hook a shop vac up to the black hose and clean the HVAC drain line. Put it all back together and then pour a decent amount of bleach down the HVAC drain line from up in the attic.

Pour bleach into the pipe with the red arrow!

This is in addition to cleaning the p-trap as mentioned above.

Above covered it. Only thing I'll add is I had a case where even after cleaning out the p-trap it drained slowly. To the point of if the faucet was on the drain couldn't keep up.

Per recommendations here, I squirted some dish soap down the drain. Then I ran the bathtub faucet as hot as it could get. Once it was hot I filled up a pitcher (or bucket) and poured it into the sink. Whatever was causing it to drain slowly past the p-trap got cleared by doing that.

Related question. I had the same thing happen to me a few weeks ago. Got the main drain cleared out, the p-trap (that's where my issue actually was), and things seem good.

Fast forward a couple weeks and my backup drain is still dripping out the side of my house. I'm at a bit of a loss.

cbminers said:

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Related question. I had the same thing happen to me a few weeks ago. Got the main drain cleared out, the p-trap (that's where my issue actually was), and things seem good.

Fast forward a couple weeks and my backup drain is still dripping out the side of my house. I'm at a bit of a loss.

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Main drain must still have a clog if your secondary drain is still dripping.

Easy fix. Thanks for the advice. P-trap was 100% blocked with sludge so definitely need to get cleaned. Now I want to do the rest of my sinks….

I cannot recommend this tool enough. This air snake has saved my ass so many times already. This tool has paid for itself 10x in the last 5 years:

https://www.homedepot.com/p/Milwaukee-M12-12-Volt-Lithium-Ion-Cordless-Drain-Cleaning-Airsnake-Air-Gun-Kit-with-1-2-0Ah-Battery-Toilet-Attachments-2572B-21/303169749

cbminers said:

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Related question. I had the same thing happen to me a few weeks ago. Got the main drain cleared out, the p-trap (that's where my issue actually was), and things seem good.

Fast forward a couple weeks and my backup drain is still dripping out the side of my house. I'm at a bit of a loss.

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do you have two AC's? If so, they may drain to different sinks.

That is an interesting tool

had this issue a few weeks back. My problem was a good ways downline and I had to get a plumber friend with his big azz snake (one with the foot pedal) on the case

Sazerac said:

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That is an interesting tool

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works like a champ.

htxag09 said:

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Above covered it. Only thing I'll add is I had a case where even after cleaning out the p-trap it drained slowly. To the point of if the faucet was on the drain couldn't keep up.

Per recommendations here, I squirted some dish soap down the drain. Then I ran the bathtub faucet as hot as it could get. Once it was hot I filled up a pitcher (or bucket) and poured it into the sink. Whatever was causing it to drain slowly past the p-trap got cleared by doing that.

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This worked for me after trying a few other methods with mixed success (replacing P trap, vinegar, drain cleaner). Although a shot or two of vinegar helps mine a lot in the months the unit is running a lot.

My A/C guy said to use 30% vinegar (available from Home Depot, etc), not bleach, for pouring down the HVAC access pipes.

I a small shop vac which just lives up in the attic. Every 6 months when I change my filters, I connect it to the PVC pipe which connects to the sink drain and run it for a minute. No issues since.