not unless your return isnt submerged. If its not you will get lots of salt spray! When you turn off your pump, the return will back syphon and drain the tank down to whatever level it is at in the tank. That would be the level it will be at in a power outage. You could fill the tank to the bottom of the return, then pour water directly into the overflow until the sump is full. this will be the correct level. experiment with freshwater till you get it just right. You can also drill syphon breaks in your return line if you want the level to be higher, just make sure they are large enough that they wont clog, and believe me, small holes clog easy! Drill them in a manner that wont cause water to spray up, and they wont cause air to get sucked in. The underside of the pipe, at least 1" underwater is best imo