Citation ST tank draining problem

[Free Ranger]

Every season when I winterize my 2014 Citation Sprinter ST, I think to post this issue for other ST owners. If I have my coach parked dead level, with good gravity feed from the drain valves to the septic and let it drain until not another drop comes out, you would think that the tanks were all but empty. On my coach that would be wrong. If I then put the passenger side up on blocks for a good six inch tilt towards the driver's side with a slight forward lean, I will drain at least another two gallons of black and six gallons of grey out of the system. The first few times I thought my tanks were empty and then found out I was wrong (surprise!) I put it up to operator error or a bad drain angle. But, I've conducted this experiment now a half dozen times making sure the rig was level and the results are always the same. So, if you have the same coach model, you may have the same issue going on.