If I can only find the ones with drainage holes, I use a pebble or a small piece of slate to block the hole. Next I place a layer of potting soil without additives in the bottom of the pot. For Echinodorus sp. I also add a teaspoon of Luster Leaf Micronized Iron. The pot is then filled the rest of the way with gravel.
Some people put a layer of potting soil, peat moss or clay under the gravel in the aquarium itself.
These are very small nocturnal burrowing snails. You won't even see much of them if the water quality in your tanks is good. They burrow through the substrate, keeping it from compacting, and eat detritus and leftover food. Unlike many other species of snail, they do not damage plants. Finally a word about substrate maintenance.