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The Background:

Shown here, the lovely setup behind my unfinished-basement washing machine. This was all installed just before we bought the house a few years ago, because the sewer is about a foot too high for the washer to dump directly into the pipe per code. Photo of existing washing machine drain and pump On the left, the discharge hose from the washer goes into the drain standpipe, through a P-trap into a drain pump, Liberty Model 404 (pump not found heh heh). The drain pump has a vent pipe on the back, which goes up and out of frame, and a discharge with a check valve (Jackel DJ-545) on the front, which goes up to to the main sewer line, just out of frame on the wall above. This is an automatic pump; when some amount of water drains into it from the washer, it clicks on with a WHOOSH and blasts the water up to drain into the top of the big sewer line - runs a couple times per wash cycle, for a few seconds each time. My jurisdiction uses the 2018 International Residential Code without amendments. Don't worry, the GFCI breaker for that laundry outlet is just across the room, though I do plan to move it a little farther from the drain pipe.

The Question:

I want to add a utility sink to the left of the washing machine, centered about 5ft from that standpipe drain. An advanced computer rendering of my plan is shown here.

Photo of existing drain setup, with planned utility sink addition crudely pasted on top

  • Can I run it into this existing drain setup, by cutting and inserting a wye-and-bend into that vertical drain?
  • I'd want to put a screw-type P-trap under the sink, to catch anything before it gets to this glued-up trap. Would a second P-trap there be mandatory, prohibited, or optional?
  • Would I need an additional vent for the sink, or would the combination of the vent on the boost pump and the not-sealed laundry drain be enough?
  • The pump is rated to pass 3/8" solids, but I can't find any similar rating for the check valve. Am I dooming this little graywater check valve and need to upgrade it to a blackwater-type valve, or is it fine for a utility sink? Don't plan to send any solids down the sink, but want to be prepared for whatever inevitably slips past the strainer.
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    Correctly? Go back in time and buy the 404L with 2" inlet. That 2" to 1-1/2" reducer downstream is bad news and a code violation in a drain. As for traps, the output of the sink trap will need to meet the drain pipe on the other side of the washing machine trap. And with the 1-1/2" inlet you'll need a separate vent connection that the washing machine can get away without, because it's close enough - but your sink isn't.
    – Ecnerwal
    Jul 10, 2023 at 1:48
  • Would an AAV work for the sink?
    – Huesmann
    Jul 10, 2023 at 12:23

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