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! 
Plumbing – Can anyone explain what this pipe is in the basement
draindrain-waste-ventlaundrypipeplumbing
Related Solutions
A capped opening in a sewer line is called a clean-out, usually they are a 4" long bend wye with a cap on one branch so you can pull the cover and run a snake down the whole length of the main sewer line.
In this case, a 2" pipe would be a good size to run a snake down to clear any clogs downstream from the toilet. I'd guess that somebody didn't allow enough drop in the sewer line and added the pipe to allow shoving the solids out of a long, level area.
Sewer Auger (Snake) or a Water Bladder Clog Buster just in case you ever have to use it.
No, it's not a vent.
Find a better store, if the ones you are going to don't have 2" PVC in full sticks (or possibly look higher up in the store you are in, and get someone to drag it down.)
In MY house, the only place you'll find 1-1/2 or 1-1/4" is the tailpieces on the sinks - as soon as it hits pipe, it goes up to 2", because it's not that much more expensive and it greatly reduces the odds of having any issue with it. I don't recall having any trouble finding it in full sticks. The main line is 4" (not 3") for the same reason. Builders looking to squeeze maximum profit don't do that sort of thing, but builders who plan to live in the building for a while sometimes do.
In retrofitting, you might need to use 1-1/2" due to space constraints. In any case, if you are redoing the pipes, you should probably bring the venting up to current code while you are at it.
Best Answer
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.