Basically a “stopper type” valve, probably shuts everything off. Will not empty both tanks simultaneously unless it has been modified. I had rear tanks on all of my boats except this Eyra which has a single tank. Still trying to get used to that, always have to remember I only have one tank with this boat so I dont run out a few miles from the ramp………96 Eyra/12 Mercury 175 Pro XS with 2015 single axle trailer2017 Victory Gunner