I imagine this is a common setup. My questions concern how the standpipe and the floor drain are trapped and connected to the sewer line. Can I know with any certain how these are connected under the slab?
I can see that the current standpipe empties into the floor drain just under slab. I suspect that the floor drain trap acts as the trap for standpipe and the standpipe does not have a trap.
I am moving the washer and dryer upstairs and the horizontal pipe emptying into the stack will be rerouted. It currently is used for a toilet. I was originally planning on using this horizontal run to empty the new standpipe into the stack but I am wondering if that will prevent the floor drain trap from being primed with water. Instead, can I run the new stand pipe line into the old one? If so, do I still need a trap at the new laundry room above floor level? If there is a trap under the current standpipe, I would think that two traps in the line would not work.