[ttiiggy]

This is 4" PVC drain line that is going to be buried under ground.
I think the same question might be asked if it was a 2" pipe in a wall.

The main horizontal pipe is going to be a drain that is properly sloped and another pipe is coming straight down vertically and connecting to this horizontal drain line.

LEFT connections in picture: Should the Y stand up and have one street 45° connected to the pipe that goes straight up?
OR:
RIGHT connections in picture: Should the Y lay down and have two 45°s connected to go straight up?

It seems like the first arrangement would make the stuff coming down in the vertical pipe splash into the horizontal drain line.
The second arrangement seems like it would be a smoother flow running into the horizontal line.

I can see where if this was a pipe in a wall, the second option wouldn't work so well because it might make the joints too wide to fit in the wall.

Are there any issues to this either way? Discussion?

 

[TheEplumber]

Both methods are okay for simple 1 or 2 story construction, but I try to use the second method when possible- it's easier to layout and keeps the main line out from under the wall and in open floor area. Sometimes mono footings are located under the wall.