leaking holding tank
Well, if I may be so bold as to answer my own question... I found that polyethylene tanks can be welded by a process called plastic thermo welding. Had a guy in a plastic fabrication company do a very nice repair, cutting out the old & fabricating & welding a new piece in place. I was v happy to give him the $75 he charged me. Might be useful info for anyone with a similar problem.