Squish them and remove ANY and ALL sacs you can find with something and let it dry out completely before you throw it away. I jst had this problem, it was SOOO bad I had to take my 3ADF and Betta out of the tank and I let my tank dry out for a few days, even had all my rocks in a strainer to dry out.. I put the rocks back in last night and started filling with water.. SNAILS!!! Coming outta EVERYWHERE!!!!
I ended up just buying new clear marble stones SOO I can see if there's any that I missed.. I put the gravel back in the strainer, and I'm still searching as to what I should do because Im afraid to boil or put them in the oven to thoroughly kill them.
((I started with one Blue Mystery Snail))
edit: I have a 15g tank.. When I drained the water, I plugged up my tub and squished EVERYTHING, filled up my tub with a big bottle of bleach, and boiled water then put that in my tub. checked again to make sure everything was squished. Drained the water, Bleached again and boiling water again. Along with Draino down the drain because my luck they'd survive in the drain or in my septic tank.