Does anyone have a good way to get populations of MTS under control when
they're overrunning a tank?

One non toxic way to nab a bunch of them is to drop a couple of big algae
wafers into the tank in the evening, right before you turn off the lights. In
the morning the wafers and surrounding gravel is usually covered with balls of
snails. Take a big net and scoop out the snails and surrounding gravel. Toss
the whole thing or pick them out and return the gravel. Do this a few times in
a row and your population will take a serious hit, no harm done to anything
else.
Good luck.
J