When you're winterizing your pool, Bungee-Plug is the only blow out plug you'll ever need! The bungee strap stretches to allow air or water to flow freely when pressure is applied. The bungee strap responds instantly to pressure relief and seals with a unique triple O-ring seal. The technology behind Bungee-Plug is so dependable, it can also function as a hydrostatic relief valve at any depth or a multi-directional return fitting.