The kind of snails that don't 'need' another snail to breed, they can usually be taken out of the tank by putting a lettuce leaf in tank. They find it and attach to it while they're eating. Then you just remove the lettuce from the tank. What you do with them after that......is your choice! There are Apple snails, which are usually bought at the fish store. They need to have 'two to tango'. Even though some times they are already preg when you buy them, and there's no way of telling. They are nice, and usually only eat the dead plant stuff, not the healthy plants. The only part I don't like about them, the water seems to dirty quickly. They are constantly eating and poo-ing. There's Threads on here about Apple snails, and others. Very informational.

You should do a 'search' and read a bit. There are some very good uses for them.