Is hole the current black tank threaded??? The flange and black tank on my '87 was threaded and you have a newer trailer than me so I find it confusing that a newer trailer would have an unthreaded black tank. Did a previous owner use the flange you pulled and just seal / caulk the flang into the black tank?
Can you provide a photo of the hole in the black tank???
Carl, Elaine & Finn The Beagle
2006 30' Classic W Slide & Limited Package Katarina
2006 GMC 2500 HD 6.6 Turbo Diesel Crew Cab 8' Bed
NQ3U (was KB3UOM)