I'm installing a front-loading washer and dryer in a room in my basement which is adjacent to a full bath and I've got a couple of questions about venting and drain size.
I'm installing a standpipe and washer outlet box. From what I've read, that standpipe and the drain back to the main should be 2". The problem is that the existing drain line is 1 1/2". When I tackle the bathroom, I will replace the whole run with 2", but that won't be until next year and I need to get the washer running in the meantime. Should I go with a 1 1/2" standpipe so the pipe is the same all the way back, or a 2" standpipe and reduce it? If so, where's the best place to do it? I have access to about a 6 foot horizontal run.
The other big question is the venting. I've included a diagram which is hopefully pretty clear. The toilet and shower seem to be on a different line than the sink and standpipe. The main drain to the street is on the other side of the house. There's a horizontal pipe under the slab that runs over to that. I'm assuming the toilet, tub, and stack in the corner all feed down into that.
If I were to run the standpipe as pictured, the nearest vent would be that corner stack, which is about 16 feet away. I'd love to hear that's enough, but I'm guessing it isn't.
The only other way that I can think to add a vent close to the standpipe is what I have pictured in blue. Because of the window and a soffit on the wall, it's got to make the two bends. I'm also not sure if it's okay that it's running into the upstairs sink drain.