Well, I/we decided that the Sealand Traveler Model 511 was just too far gone to keep.
So we got a Dometic Aqua-Magic VI and I installed it. New floor flange and then the problem arose with the black tubing to standard 1/2" Inside diameter hose.
Seems there are no fittings available at Ace or other outlets like it. "Special" RV fittings required. PEX and standard won't fit.
So I used my Rube Goldberg theory, my 1/2" drill, and my small belt sander. I tried PEX (too small) and standard 1/2" brass barb fittings (too large). So I chucked up the 1/2" barb connector fitting and belt sanded down one end until I could push it into a piece of black tubing. Then I smeared some tank sealer on the barb. Pushed it into the black tube and then used a standard hose clamps, along with 1/2" reinforced hose. Works great. No leaks.
Wait....you didn't use Shoe Goo?
You don't think I would waste my good Shoe Goo on a toilet, do you?
No duck tape??
With coaches, especially those that are 30+ years old, one needs some imagination, where-with-all, and a couple large boxes of miracle substances like shoe goo, tank sealer, JB Weld, Dicor, gasket sealer, super glue etc. etc. etc., and, of course, electrical tape and duck tape.