Go get yourself a zucchini, cut it 1/4's. Leave it raw. Get 4 forks stick a fork in each 1/4 of zucchini. Place in the bottom of your tank. Check for snails in the morning. Discard snails. Repeat process until you can tolerate the # of snails in your tank.
It's an on going process but what I have found to be the most effective. To discard the snails, I used to scrape the snails off the zucchini and use them as Clown Loach food, after the first 24 hours then put the zucchini back in and use it again for 1/2 a day. (I wouldn't leave the zucchini in the infested tank for more then 36 hours because it starts to fowl the water.) Then I'd take the snail covered zucchini to a 75 gal. with a bunch of Clown Loaches and Plecos and watch the feast.
Now I just keep assassin snails in all my tanks. Btw, I have found that Clown Loaches do not eat assassin snails.