The isopropyl (rubbing, IPA) alcohol you buy at the super has as much as 30% water in it.
You can find >99% reagent or pharmaceutical grade isopropyl at your pharmacy or scientific supply.

I've never considered using alcohol for cleaning the sand. If I were, I'd probably switch silane instead and have done with the whole problem.

Hard to beat a cheap turkey roaster filled with sand at 400F for an hour.