Wow. Much more difficult day than anticipated. Clog in the outlet riser to tank resisted every tool so had to ram through it using prop puller to force steel rod through to top of bronze pipe. Quite messy despite careful prep. I'm still fearful that part of clog remains so I'm getting some muriatic acid in the morning to flush through the system. Bill Rouses drawing  of the holding tank plumbing  was important; needed to be sure the end of bronze pipe in tank didn't contain a bend, which would have complicated my brute force solution.