How to Clean a Condensate Drain Line

A central air conditioner‘s condensate drain line is crucial to its functioning.

That’s why you need to perform routine maintenance to prevent it from clogging.

We’ll talk about how to do that, but first, it’s important to understand how central air conditioning works.

2 ac units
Air conditioners keep the inside of your house cool and the humidity low.

All About Air Conditioning

In addition to cooling your home, an air conditioner removes moisture from the air. This process lowers the humidity level inside your house.

Any excess condensed water is removed from the air conditioning unit through a small drain pipe that extends from the indoor air handler to outside your home. This drain pipe deposits the excess condensed water outside on the ground.

Walk outside your home and look at the condensate drain line. At any given moment, especially during humid weather, you should see water dripping from it. That’s the drain line in action!

Now, if you don’t see the drain line dripping, chances are, it’s not draining. And that’s a problem.

a plugged condensation drain
The condensation drain needs to be free of blockage to keep your AC running smoothly. (Adobe Stock photos)

Unclogging a Condensate Drain Line

Over time, algae, mold and mildew can build up inside the condensate drain line and form a clog. This causes water to back up and overflow inside the air conditioner unit.

Preventing this from happening couldn’t be more important, and fortunately, maintaining your air conditioner’s drain line couldn’t be easier!

Just pour a cup of bleach in the drain line’s access opening near the indoor air conditioning unit. This will kill any algae, mold or mildew that has formed in the pipe.

If the condensate drain line is clogged, you will need to use a wet-dry vacuum or a special pump to unclog the line.

Watch this video to find out more.


  1. I have a new home 1 year old . I went in the attic to put a cup of bleach in the pipe they showed me when I bought the home. Before they always had cap on the pipe but this dose not. Is that normal? second thing is cold was blowing out the pipe. Is that normal? I would very much appreciat an answer. could you e-mail it to me. thankyou Dorothy

    • Hi Dorothy,
      The port in the air conditioner condensation line in our house didn’t have a cap on it either when we bought it. I bought a cap at a home center for a buck or two to fit the PVC line on my unit, put it on, and it’s worked fine. I don’t think it was that bad not to have one in my case, since the unit was in a closet in the house, but if your unit is in the attic, you’re probably losing some of your cold air out the vent line. Also, it can keep any mice or bugs from crawling into the unit.

  2. Ok. my a/c units drain into a pvc pipe that is tied in to the house’s plumbing. I traced the pipe through the attice and both units go into the large PVC pipe that goes down the wall and up out of the roof to the vent stack. Nowhere to put vacuum to suck out clog. Any suggestions of how to clear clog from the access opening, which has water up to the cap itself.

  3. I’m having water drip from the pan under the unit in the attic. I found the two pvc pipes coming out of the unit along with a copper pipe that has quite a bit of air flowing out around the opening. However, neither one of the pvc pipes have a “T” to open and try and unclog. Any ideas would be greatly appreciated!!

  4. My air conditioner is leaking… I got under and vacuumed inside behind the filter, that is where the water was leaking. I attempted clean out the drain pipe with a vacuum and then I poured the bleach down the drain. I hope this works!!!! I will let you know.

    • Hi Jim,
      Click on the “special pump” link in the article above, or the “Innovative Pump Unclogs AC Condensation Drain Lines” article link in the Further Information section above, then click on the Mighty Pump link in the article to go to the website of the company that makes it where you can purchase the pump online.

  5. My pvc pipe goes into a box (at this moment the box is full), and then a piece of flexible tubing goes up into the rafter of my basement across the ceiling and down into my laundry tub. How can the water run up? It’s been working fine for five years, but as of this moment water is leaking from the pvc pipe. It’s leaking from where it is connected to the ac unit in my basement. Before the pvc pipe went down and across the floor to my floor drain. Tomorrow I am going to disconnected this box and see what’s up. Any comments/advise would be greatly appreciated. Thanks!!

  6. I want you to know, I fixed the leak in my a/c. I finally broke down and called a plumber and explained the problem. They came out and he took the metal lid off the unit. There was water standing in there. He tried to tell me I needed a new coil. We poured water in to the pan to see if it would drain outside. There was quite a bit of rust and the particles and water slowly started to go down the pipe. He told me to turn the unit off for a couple days and he would be back. I still wasn’t convinced the pipes weren’t clogged. After letting it dry for a couple days, I took the shop vac and blew the pvc pipes and vacuumed out the pan for any remaining rust particles. I sealed the corner of the drain pan with some very duty seleant, turned the unit on and it works perfectly. I think they a/c guy just wanted to make money off me as he told me blowing out the pvc lines wouldn’t work. Bottom line, it pays to do it yourself!

    • Hi Lucy,
      Glad to hear you were able to fix your dripping AC pan, and thanks for following up to let us know how you did it!

  7. I have a drain from the A/C to a PVC line that is connected to my bath drain. It was recently unclogged and now when the a/c is on, we hear a flapping sound like a check valve closing. Any idea what it is or how to fix it?

  8. Hi,
    My house has 2 A/C units.There are 2 pipes running outside the wall (roof level for the first floor and at the floor level of my second floor) where water is dripping slowly. My neighbour scared me saying those are the backup pipes for A/C water drain and the water is never supposed to come out from there. Can you help me understand if that’s true?? My house is 2007 built.

  9. Hello, I. Recently moved into a newly constructed house and found that a substantial amount of air is being blown from the water drain lines coming out of the unit. It is stored in the attic and the attic space is cool upon entry. Is there anything that I can do to keep the air from exiting the line?

  10. what about if you are on a septic system? boiling water maybe? I just have heard its not good to put much bleach into a tank?

  11. I was told not to use traditional bleach in the drains, but a mod one like Greenhouse chlorine free bleach …or even white vinegar… you tell me! In any case, how often can I do it?

  12. I had my home built in 2000 year, since I have had a light powder falling into the whole restroom, on the sink, on the floor and everywhere. I have brought in an dry wall contractor and he said it was not the dry wall. I then had an air conditioning guy come and he installed a very expensive air filter that cost $2,500.00 he said it would help pick up everything, well I still have the problem. what do you think could be causing that thin powdery particle all over my rest room?

  13. Possible leaked around your ceiling AC booths where the air velicity out of your registers is pulling air around your booth caulk. Remove the grill and caulk around the booth.
    Cowart’s Heating and air

  14. Can a condensate line coming off of the furnace to the floor drain have it’s vent pipe covered with duct tape on the top? This is what a service tech did to the vent. I have been trying to get an answer from the furnace company as to why this was done,. So far I only get the run around and no answer. I removed the duct tape. The service person was there to do the winter maintenance. He didn’t even bring a vacum with him,

  15. Hi I have a problem with the L galanized bracket that my plastic tubing for the AC condensation comes out of my inside furnace unit. How can i unclog that L bracket. Is there a way to pore vinegar into the AC pan which should be right beneith the furnace plium> I replace the plastic tube that runs from that L bracket to the drain. Please advise.

  16. Hello, yesterday I went in my garage and noticed water all over it was dripping from a T shaped plastic pipe located at the bottom of the furnace. I turned off my. AC and the water stopped dripping. Looking at the internet it must be a clogged draining pipe. Every video that I looked at the draining pipe was out side and it gets unclogged with a vacuum, I circled the and couldn’t find a pipe, I looked everywhere couldn’t find it. The only pipe is inside my garage attached to the furnace, can anyone help me out? Thanks.

  17. DO NOT, I repeat DO NOT USE bleach. The bleach can and will EAT AWAY your evaporator coil. Hot water under suction is the ONLY manufacturer approved method of condensate drain cleaning.

  18. Definitely dont poor bleach down there when your furnace or ac is running or about to run. Unless you want a face full of bleach. Also that wonderful bleach smell is going to work its way into the air handler and therefore throughout your home, lol

  19. Bleach, diluted, is ok to use but NOT on coils and only on PVC piping. As she shows in video, ok to pour it into the vent pipe. Do this once a year. Also, her video does not show a P-trap or overflow line coming from the unit – strange. This overflow line should go to a drain pan under the unit and then the open drain line to the outside.

  20. does a water condensation line have to be vented for the water to drain/
    the line is a 3/4 pvc with a drop loop.
    can just gravity allow the water to drain/

    • Hi, Dan! A wet-dry vacuum often is needed, particularly with clogged pipes. In that case, gravity would not work.
      Thanks for your question!

  21. Hi
    We live in Lake County California and there are several wildfires right now all around us. We were evacuated for five days and just returned home and are being evacuated again today as i write this. The reason I’m writing is the particulate matter in the air is very high meaning there’s a lot of Ash floating and heavy heavy smoke. My air conditioning unit started acting up and was no longer blowing cold air, it was barely blowing at all. I took the unit apart, it’s a manufactured home, a fancy name for a new newer mobile home. okay the heating and air conditioning unit is inside the house with the outside blower condenser I guess it is. I cleaned the coils and I noticed Rust and standing water at the base of the coils I used a fine metal brush actually it was a dog hair brush to clean the and I think that worked pretty well but I am unsure of how to unclog the drain because I don’t see one I put baking soda and vinegar in the tray that goes around the coils several times and cleaned as much of the rust as I could. it was 102 today and, the fires make it completely unbearable, so I had to admit defeat and put the unit back together. it is now blowing cold air, but not as strong as I think it should be blowing. I don’t know what to check next. I just had spinal fusion surgery so my range of motion is a little limited. As far as climbing under my house I think that’s not going to be possible I just don’t know where the drain is or how to identify the drain. As I said, my main unit is in the house and I think it’s the condenser that’s what it’s called is outside how often would someone replace or should someone replace the heater air conditioning unit I guess it’s kind of a moot point right now as we are being evacuated hopefully we will be home in a couple of days and the air conditioning will magically work again. How do you identify the drain? Can I just drill a hole in the base of the frame around the coils? It would then drain onto the ground under the home.

  22. This design is spectacular! You most certainly know hoow to keep
    a reasder entertained. Between your wit annd your videos, I was almos moved to sgart my own bllog (well,
    almost…HaHa!) Great job. I rreally enjoyed whwt
    you had to say, and more than that, how you presented it. Too cool!

  23. Do I need to worry about this condensation pipe in the winter when heat is on? Is their another solution besides bleach you can use? Would that be white vinegar?


    • Hi, Joe,
      Danny says, “No, it’s not something you need to worry about during the winter; only when your AC is being used. I recommend sticking with that cup of bleach, too. Thanks for your question!”

  24. I recommend using vinegar less corrosive than bleach especially on aluminum evaporators!The pvc t will allow liquid poured down to back feed into evap pan witch is good,but not useful when using bleach.

  25. To the commentor who says you don’t need to worry about it in winter NOT TRUE. high efficiency hvac will generate water when in heating mode

  26. If I have a clogged condensation line will this cause my air not to cool I was told this from a company that came out they stated my line is clogged and my air still comes on but not getting cold when I turn. Off and let sit for a few hours it starts back working wth!?

  27. Just watched the video! Went an seen just that!! With the help from son my ac is running again! I also, used my shop vac! To clear the line!! BUt, I realized That I have fix that problem! The line at the end travels up!! So, Since I know a bit LOL! Will be installing a new line that flows down hill! Thank you so much!!

  28. What they don’t tell you is that the disposable filters you use, shed and that clogs the drain tube as well. The cheaper the filter the more shedding and that builds up over time. The vacuum isn’t getting all of that out. So depending upon whether you can flush it with a garden hose from inside the house or garage at the air handler, you may have to back flush it from the exterior drain outside the house at the compressor. Other debris, like dirt can become mud if the drain is coming out of the ground instead of thru the wall.

  29. I have no way to access the drain pipe. There is no where to open to unclog the trap or dump vinegar in it. What do I do instead? Dump vinegar in the tray itself and hope it goes through? Having an access point in the pvc pipe would be great. They just didn’t make it that way.

  30. My condensation drain line drains into a 2″ pipe that has a trap, it then runs down and across the ceiling and into my bathroom into a 4″ pipe then out’ The line backed up today and ends up soaking my bathroom ceiling, I remove the small line leading from the 2″ line and place it in a bucket to drain into. The part that baffles me is why it’s taken this long before it’s backed up, the A/C has been running for weeks, I’m almost to the point of calling a plumber and have him run a snake into it. What do you suggest I do?

    • Hi, Roger!
      We’re always looking for homeowners to call into our radio show and ask questions directly to Danny and Joe. We’ve reviewed your question and shared it with our radio producer.
      Take care. 🙂


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