I have noticed over the years on a few boats that the tank would not fill up all the way and would slosh when tacking. Did not happen often but not sure if that is the case. I use to make sure the seal on the bottom of the water intake or the circular piece of metal welded to the rod with the wing nut was on good, got several folks on board to add weight, filled it up or added water from inside with a hose and in most cases that stopped that sloshing. This of course there were no other issues of water inside the boat. There is no vent for the tank except under the bottom step inside the boat adjacent to the wing nut.