I want to add a tee coupling to my existing AC drain line to accommodate the drainage of newly added dehumidifier condensation water. I did some research myself and debating between using a saddle tee or a regular tee with a telescope coupling. I lean towards the telescope coupling because it offers a cleaner installation, eliminating the need for drilling and potential debris left inside the PVC pipe. However, I'm concerned whether the telescope coupling might alter the natural downhill tilt of the drain pipe, potentially causing water trapping issues.

What is the best way to accomplish my goal?

Edit: my furnace features two 3/4" drain lines: a primary line, complete with a clean-out, and a secondary line. I am thinking about connect my dehumidifier's drain line to the secondary line. The dehumidifier's drain line is from a 3/8-inch vinyl tubing from a condensation pump.

  • Given that most AC condensate drains are barely big enough, if that, adding to it may be unwise.
    – Ecnerwal
    Commented May 5 at 16:15
  • But a condensate pump is typically an intermittent load.
    – Huesmann
    Commented May 6 at 11:41

2 Answers 2


You didn't indicate the size of the drain line. Most are 3/4 inch. Use a saddle that allows a 1/2 inch line.

Assuming that, just glue the saddle and drill the hole. Follow that by flushing the line with a cup of water. Attach you drain and you're done.

A side note: Some locals don't allow splicing another drain line into an AC drain. Research if you are allowed that.


Good idea to use the secondary line. Don't use the primary. I don't see many pros and cons of different tees for this case. Do what works for you. I would do what's cheapest. Note your dehumidifier needs a trap to keep it draining continuously. Without one it will randomly fill up its bucket and stop. With a vinyl hose you can make a trap by making a loop at the exit from the machine.

Also, where you tee into the PVC, make the new vertical piece high enough to be above the top lip of the secondary drain pan at the A/C. That way, if the secondary drain is blocked downstream, the dehumidifier condensate will back up into the A/C's secondary pan rather than the floor. Put a leak detector in the secondary pan if you don't have one. Now that the pipe will be in regular use, it will get blocked. Blow it out when you blow out your primary.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.