I bought a house and see this in the laundry room, how should i connect my washer drain to this? Do I need to thread a PVC pipe to this first and let the pipe go up so i can put washer drain on the pipe? Thanks
No. That is a drain for a drain pan.
It's not a washer drain.
Normally this is what you would have in the wall.
A 2" standpipe with p-trap, vented through the roof, with a hot and cold supply and water hammer arrestors.
That gray box on the left is the dryer venting.
This is a second floor installation, so you see a vent from downstairs tying back in at 42" above the floor.
From a plumbing standpoint, I can't either.
That looks to be a 1" thread on there for a drain pan that sits under a washer and collects water in case there is a leak.
If it's my home, I'm pulling the drywall off and taking a look to see what's up.
Is there a laundry tray nearby that the washer may have drained to?
That looks like a PVC pipe with an NPT (MIP) thread. How big is the internal diameter? That will probably measure just a little larger than the nominal size.
Does that pipe maybe go to the yard rather than the sewer system?
Based on typical shoe molding size, that pipe is not even close to correct size for a washing machine drain (especially the new ones). Located that close to the floor makes me think it's for one of those plastic drain pans, as Terry mentioned above. Maybe the washer used to drain in the laundry tub, if there is one?