A Question about AC Drain Connected to House Plumbing

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Best to remove the p trap. Clean that and snake the line a little ways. It’s easy.

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Thanks. Sounds like I have an evening project.

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Only if there is a blockage that allows the water to back up higher than the P-trap.

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Makes sense. I guess the 2 are unrelated but, the timing is a bis suspicious.

Don’t pour bleach down the drain. Chlorine fumes will attack the aluminum in your AC.

that is why you run the condensate to a vent and not a trap drain

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My last guess is that the washers in those 2 fittings are bad and allowing water to back up through them?

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Sure can. Or you have stripped the threads.

ours did this last year, same exact thing. Problem is where it goes to that sick is my kids sink(teenagers) so no telling what they are putting down that sink. I did buy one of those plastic snake things and he has it now. I remind him every so often to just run water and run that thing in there if he notices his sink is slow.

I've since signed up for a 2/year AC/Heater service and they check it every time now.

But yea apparently that clog was bad.

Also I was told not to add bleach? I need to ask what is a good substitute. I've done bleach as well.

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Also I was told not to add bleach? I need to ask what is a good substitute. I've done bleach as well.

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Vinegar - cheapest you can find. A cup or 2 each month during cooling season for maintenance. But I’ll use bleach when I have a clog in the line, but clogs have always been downstream of the vent tube in the condensate drain line and not too close to the evaporator coil.

The box stores like HD have a stronger version of vinegar (10% acetic acid, regular household is 5%) but it’s kind of expensive - at least I think so…..lol. .

Well, I've done all I can do. Replaced the washers and the fittings where the leak is occurring. Same issue, just a glass of water poured into the sink backs up to the connections on the tail piece and leaks into the bucket i have in place.. Makes no sense, doesn't look like enough water to even reach where the pipes meet the wall.

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Well, I've done all I can do. Replaced the washers and the fittings where the leak is occurring. Same issue, just a glass of water poured into the sink backs up to the connections on the tail piece and leaks into the bucket i have in place.. Makes no sense, doesn't look like enough water to even reach where the pipes meet the wall.

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OK - I had exactly the same problem as you for a good while. I tried snaking the bathroom drain line etc. without success. This is what worked for me. On the advice of an old guy at the hardware store, I used “Liquid Fire” (strong sulfuric acid) poured down the sink drain after removing the p-trap. Follow the directions on the bottle as to the amount and procedure - use gloves, eye protection, etc - be very careful! You’ll probably need a funnel with a hose extension to shove partially down the sink drain when adding the liquid fire.

That cleared the sink drain and prevented water from backing up. However over time it would re-occur, and I’d have to repeat using the liquid fire, which I really didn’t like doing. Then I started adding a couple cups of household vinegar to the HVAC condensate drain monthly during the cooling season, March-Nov. And for good measure I I pour a gallon of vingear down the bath sink, that would back up, monthly (generic vinegar at the grocery store is cheap) right after dosing the HVAC condensate line - whether that’s necessary I don’t know, but since vingear is cheap I do it……lol. .

I have not had a re-occurrence of the bathroom sink backing up with water since I started doing this a couple years ago, nor I have an issue with the HVAC condensate line not draining and overflowing into the secondary drain and shutting the HVAC down until I could clean the condensate line.

In my case it is definitely associated with HVAC condensate line which is plumbed into the vent stack associated with that bathroom sink drain, I suspect that is your case as well. Up to 1 gallon of HVAC condensate water per hour can produced by the HVAC - so any obstruction or partial obstruction in the drain line from “slime” caused by the continual release of HVAC condensate water into drain line can cause the backup in both the HVAC condensate line and bathroom sink you are experiencing ……as I’ve learned at my house.