Great solution. My 2008 Classic has the plastic Thetford. I would like to replace it with a china bowl model one of these days. I'll remember this tip incase only the round one fits.
2008 Classic 25fb "Silver Mistress"
2015 Ram 2500 6.7L Cummins. Crew Cab, 4x4, Silver
2010 Tundra 5.7L, Double Cab, 2wd, White