I'm not sure of best approaches to installing a bottom drain, but I'd
adopt the attitude that it *will* shift and leak unless you do
everything to prevent that. That way, you've probably done all you
can. It's probably the last place you want a leak.

Hal, I totally agree with you about the difference in effort to work a
knife gate vs. a ball valve. I suppose I could have just added a ball
valve at the supply side (where stones might enter) for emergencies,
and a knife gate after that for routine use. I really felt the need to
have a positive shut off on the supply line, and then I switched out
my other valve for therapy.

Dave