We just bought a house and are getting a new washer/dryer setup, but the old one is slightly confusing. There is a switched pump to pump out the laundry water. I don't know if this open pipe above the washer is a vent or if it was just the old homeowners way of initially tying into the sewer line prior to the installation of the pump. It looks like it has a P-trap, so I'm not sure if it is a vent or the initial drain attempt. This is in a basement below grade and main line, so I know the water must be ejected upwards. Does anyone have any ideas on this pipe and if I can get rid of it when rerunning the new drainage setup? I am thinking of a laundry sink with an auto pump, a check valve to prevent backflow, and a ball valve to limit flow and prevent the pump from burning out. Thanks so much for any help you can offer! enter image description here

  • I would agree that looks confusing, at first glance I thought that line with the P trap was for the washing machine but it is on the discharge side of the pump with the intake spearing to come from the basin , if everything is working now where is the water going? Dose one of the fittings go through the wall as a drain? We can only see what is in the picture but there are several fittings I can not see what they are possibly a typo of T or X fitting with some of them plugged?
    – Ed Beal
    Commented Apr 7, 2020 at 13:17
  • 3
    Perhaps the previous owners had the washing machine stacked on a dryer...
    – Solar Mike
    Commented Apr 7, 2020 at 13:27
  • What is up in the ceiling? Any clues there?
    – JACK
    Commented Apr 7, 2020 at 14:49
  • Where the pipe goes into the wall (near the left side of the T) appears to be the main drain line. The pipe to the right of the T is sloped upward at 1/4 inch per foot as it should be, but I just don't understand why you would have the pump and the open pipe for draining the water from the washer. In a nutshell I was going to switch the two 1/2 vertical water lines to PEX. From there, I will have a split to a 3/8 line for the sink and a 3/4 line for the washer. I just wanted to see if anyone had any immediate thoughts on whether that piping configuration was necessary.
    – Brandon
    Commented Apr 7, 2020 at 18:24

1 Answer 1


Without the sink and pump, usually the washing machine discharge hose would be inserted in the top of that open pipe. It is above the level of the exit pipe, and has a trap to prevent outgassing.

I would think the pump would have a similar connection (e.g. connection above drain with trap), if there were other users of that drain line. But I guess not in this situation. Perhaps that was added later.

  • 1
    The line going up to the P trap is coming from the discharge of the pump. Clearly there is either something not obvious from the photo or this is a recipe for a mess as I believe the pump would overwhelm the trap and blow water out the top of the vertical pipe.
    – jwh20
    Commented Apr 7, 2020 at 15:16
  • Excellent observation
    – DaveM
    Commented Apr 7, 2020 at 15:51

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.