Drain line attaches after sewer trap

Question

I'm trying to understand the route taken by the drain colored red in the images below. This drain starts nearby in the my garage where it is attached to a sink using this drain pump. What is strange is it seems to intentionally connect to the sewer after the U-trap / cleanout which all other drains in the house flow through. I say "intentionally" because the pipe could have taken the route in blue where it would use less pipe. Maybe it is related to sink drain pump?

I'm putting shelves in this closet and would like to move this drain to take either the blue route or the orange route to make it less in the way.

I'm leaning toward the orange since that keeps it most similar to what exists, but I dont understand why the blue route was not taken all along.

Answer 1

I haven't seen that setup before but digging a bit it seems like they are called building traps or running traps and they were commonly install pre 1950.

On the surface it is an interesting idea to prevent sewer gas where it enters but the problem comes in when they clog. Traps do clog and the last thing you want is the only sewer outlet from your house to clog. Individual traps may clog but at least the whole house isn't out of service. A clogged running trap might not be noticed for a while since it will be at the lowest point of the plumbing system. A clogged individual trap will be noticed at the fixture in use.

I had a main sewer line clog and an unused toilet and bathtub at the lowest level. I had the water supply to the toilet shut off. The sewer backed up into the tub, clogged the tub drain and then backed up the toilet bowl onto the floor, it also backed up into the toilet tank and up the kitchen sink drain. The basement wasn't inhabited so it was a few days of 5 people using the house before discovery. Try to avoid at all costs. I didn't even bother trying to clean the toilet. Put my full face shield and sledge hammer to use and put the pieces in the garbage.

One disaster avoidance technique is to have a bathtub at the lowest level so that in the event of a backup it goes into the bathtub, doesn't overflow out of the toilet bowl onto the floor and can be cleaned up relatively easily.

You should get rid of that trap - crazy someone installed that in 2000!