Good to find this item (#10 neoprene stopper). Usage will be for a non-scientific process. Need to drain a 75 gallon gas tank in a boat that had the gas cap inadvertently left off during rainstorm. Water needs to be removed and this will be done via a siphon action into a large container. It's here that the stopper will come into play. Gas / water out of tank into container. Over fill should be good gas that'll go into standard 5 gallon gas cans.