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.

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  • "I was planning on using this pipe to empty the new stand pipe into the stack but I am wondering if that will keep the floor drain trap from being primed with water" Why would using the horizontal pipe (currently for a toilet) have anything to do with the floor drain pictured? How would that have any effect? Please clarify your question. – Jimmy Fix-it Nov 27 '15 at 17:31
  • I was not clear enough. Fixing now... – Evil Elf Nov 28 '15 at 13:51
  • I think I am quite sure that there is no trap for the existing stand pipe in the basement. Or simply empties out into the floor drain and the floor drain has a trap for sewer gases. Do I need a trap upstairs if I am simply going to tie the drain into the existing stand pipe? – Evil Elf Dec 29 '15 at 13:06

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