I used Panacur C to get rid of leeches in my tank. I put 1 packet into a jar with 100ml of water. Then dosed 10ml on the following schedule. This did kill my pest snails as well.
Shake the jar and use a syphon/syringe to get 10ml out. A pharmacy can give you a child dosing syringe.
Initial dose
24 hours later
48 hrs later
7 days after initial dose
7 days
7 days
1 month after last dose
1 month
1 month
I didn't do any water changes along the way, to keep the medicine in there. Hope this helps.