Quote Originally Posted by MLA View Post
The Tsunami hand help pump is a live well aerator pump. They push water, but will not suck it. As soon as the water level drops enough below the impeller, flow stops. I believe the integrated pumps are also aerator pumps. So this is also why some water is left in the sacs. However, one aid to get a more complete drain, is to use a quality check valve in the vent line. This prevents air from replacing the drained water and makes the sac "raisin" in on itself, forcing more water to the drain port.
Good point on the check valves. They work great for that "raisin effect".