We're moving our washer from our current location (hallways closet) out to the garage. To do this, I need to put in a new standpipe and drain in the garage.
The ideal junction for the new drain (green line) into the main would be in a spot that's currently a rats nest (red circled area) of various pipes. There's the drain, but also various hot/cold water lines, a gas line and heating ducts. Kind of a nightmare.
So it looks like it'd be a lot easier to have the drain go past that mess then 'u-turn' back into the existing drain for the washer. The added bonus is I'd also have better slope by tapping into that point.
Is there any reason why this shouldn't work? Is there some law of drain physics I'm not aware of that frowns upon u-turns?
Sketch (top view of the crawlspace drains):