Time to pull the cap off the mystery tube and chase a wire down it to see where it goes...
Might be set up to vent out the bottom, it just isn't open?
Also, be sure the drain line is OPEN and working before putting the washer in....
same for the hot/cold lines.
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