Looks like Camco took all the best features found on dump tanks and put them into one below. I tried 2 wheel dump tank once and sold it after first time I tried to move it on sand.
1. 4 wheel design
2. inside of tank drains toward gate valve on side. The Thetford I have it's hard to get all water out of. I added gate valve to drain hose to prevent accidents at dump station.
3. 2 clean out ports, one in flush that sprays water in all directions inside tank and other is quick fill.

http://www.camco.net/tote-tanks/rhin...6-gallon-39007