Getting rid of bush snails?

[nhbeek]

48 hour drowning, repotting + washing, and malathion have been effective enough for me to eradicate them in a medium sized collection.

I found that the concentrations of carbaryl (sevin) available at the store only sickens the snails, and does not kill them, but just a 1/2 tablespoon of concentrated malathion per gallon of water kills them instantly.