The head is plumbed directly to the holding tank. My holding tank has a top discharge fitting (i.e., a tube that extends from the top of the tank to within 1/2" of the bottom) so it can't leak out a fitting. From the tank discharge the hose goes to a Y-valve with one side connected to the deck pumpout fitting. The other side goes via a whale pump to the seacock. To pump overboard, you just set the Y-valve accordingly, open the seacock and pump the whale pump. I also only use fresh water for flushing. My head intake is plumbed to the head sink drain. I generally keep the sink drain seacock closed. So flushing is done by putting the appropriate amount of water in the sink, then flushing. The system has worked very well for the last 15 years