I had that problem with a TT with the black tank. When I took it back to the plant for some warranty repairs I handed the plug (knock out) to them. You should have seen the look on their face. I told them that I had rinsed the crap off it so it was a lot cleaner than when I had to reach up in the valve and pull it out
Dean & Cindy (Go DAWGS)
2013 Ram 3500 CC DRW 4.10 "Plain Jane"
(RIP "Struck by Lightning")
B&W 3600 Hitch 25K/6.25k
2012 36RL, Disc Brakes, G614's, 7K axles, Combo WD, Awning Toppers
Full Time Since April 1 2015:)!