Hi everyone. I'm new to the "ask me" site. But I my situation is this. I just installed a washing machine on the second floor of my house. The pipes are all connected and ready for use. So I turn the washer on and the water wnet down the drain and drained fine for like 30 seconds. Then the water came back up and out the top of the drain. Why did this happen?

Is that drain something you just installed to? I assume it's a trapped stand pipe, right?

Yes I just instaaled it. And yes it is trapped but I don't know why. The drain is not clogged at all.

"the drain is not clogged at all" apparently this may not be correct. If your main was clogged your seconf floor washer would push back into your first floor fixtures, and most 2nd floor fixrures for that matter. I would run a snake down that line after removing the trap, if that's possible

Is it possible that the drain needs an air vent and if so, can I install one that doesn't need to go through the roof?

No its not just possible, its required by plumbing code. Basically if you have a drain you need a trap, if you have a trap you need a vent after the trap. Does your local code allow for the use of an AAV?

What is an AAV?

Air Admittance Valve can be used in place of a ventstack but not always allowed by local codes. AAV for Washing Machine Drain - Home Repair Forum

Hello mikida. Did you install a washer box by chance? If so, is there any chance when you knocked out the cover plate on the drain, it fell into the drain? This could very easily cause a clog in the drain.

No I did not install a washer box. But I'm going to try this AAV and see if that works. Thanks to everyone. I'll pay it forward. mikida

Mikida...

Check out the diagram below for proper installation/location of an AAV on a washing machine drain.

The standpipe out of the PTRAP should be between 18-30" (ignore the 30" minimum standpipe as noted below).

Good luck!

Mark