If you have a leaky dump valve, it may be that you are leaving the valve open when hooked to a dump station. it is ok to leave the shower valve open but not the kitchen. if it drains slow as you use the sink it lets junk get in your valve gasket. This prevents it from closing good. only dump it when you have enough water in it to have a good flow as you dump. this prevents sedement from filling up the gasket.