What I did (kinda by accident) is dump it and some water in a baggie. Let it sit for a few days and the body decomposes very fast naturally. After a few days give it a good shake and everything will come out. It will stink to high heaven so DONT open the bag inside. I left my shell outside and now that it’s dry they have no smell.
just did this yesterdy.. i let it sit in a jar for almost a week, thn uuses tweezers to remove snail...gross..and sad, but then i washed it wih very hot water, them soaked it in taank water then sniffed it and put it in tank.