DRAIN-O flow-thru plugs are designed for max-stretch, no matter the size you choose. Each plug is designed with special features that help keep DRAIN-O in place.DRAIN-O has a pencil-thick airhole vent through the centre of the plug—the design helps “equalize” the pressure inside and out. That feeling you get when you want a plug to stay put but your muscles want to expel it is partly built-up pressure behind the plug—this feature helps with that.