Google for Hepvo waterless valve...this is a device that replaces the usual P-trap in drain lines. Used to save space below sinks/showers, etc. It has a design such that if you run a cleanout device thru it and pull it back, it will destroy the valve.
As far as hooking up the washer, it works just the same as a P-trap, you just can't use the normal pass-thru cleanout tools.
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired