Lou and others interested:
I don’t as yet tumble myself, but the wholesale caster I use has
a system he designed. He has three tumblers set side by side in
a rack made from 2x4’s. The bowls are tapped as you described.
Untapped bowls are considerably cheaper than tapped ones if you
are buying. An aquarium type tubing hose leads from the bowls to
a 5 gal bucket below and in front of the rack. Above the
tumblers are three other five gal buckets which are tapped and
have stopcocks so the drip from them can be regulated. There is
no recirculation; I think you would find that in one tumbling
cycle a 5 gal bucket will more than hold the amount of flow thru
liquid needed.
If you have questions about the niceties of how this works, I
will ask.