Maybe you have had the same problem the head keeps backing up after you have pumped the waste or water out. This was happening to me so I asked around and the normal solution is to replace the joker valve. At the same time the pump plunger was taking maybe 15 to 20 strokes to bring water in and then take the waste out. I looked into that also as after checking things out with the manufacturer I learned I could order a new pump assemble including the joker valve for about 41 dollars. So I decide to do the whole assemble the joker valve alone was $14 dollars at West Marine so I think this was a great deal. In addition the new pump assembles have a locking handle to eliminate the back flow issues. 10 day later the assemble came in and man was it easy to switch out. All I needed was a screw driver:

1. First pump the bowl down as far as possible
2. Then disconnect all the hoses except the waste hose
3. Then put some towels down and under the waste hose
4. Disconnect the base of the pump first before you disconnect the waste hose
5. Disconnect the waste hose ( I had zero leakage of any waste)
6. Take the old assemble off and reverse the process with the new assemble.
The total time to do the job was 30 minutes. The new assemble works great only maybe 5 strokes to move the waste and bring in water. Just a side note I ordered a couple of joker valves from the manufacturer for the future they are only $4.50 each if you get them from the manufacturer.
So that is it an easy to do project.