First of all my tanks drain from the center (longitudinally) at the bottom/side. and the tank is formed so that it slopes in all directions to that point.
You should get underneath and figure out where your tank drain really is. Dont assume it's at one end of the tank and that raising one side of yout MH will empty it.
I agree with all of those that have written that this is an answer in search of a problem...you really dont have a problem. Leave it alone.
The way I handle the tanks is that I do not even hook my drain hose up at sites. I keep all the valves shut and let the tanks fill completely. Then, and only then do I dump them. This means that you always have more than enough liquid and far more pressure to dump those tanks clean.