I don't have the experience you are asking for, but I do have a SaniCon and you don't neet to worry about tank force. It is a suction system, after you open the drain valve and let the liquid fill the Sanicon 3" hose, you turn the motor on. Then the Sanicon motor sucks the waste from the drain opening into the motor impeller and then out through the hose.
Sounds like a simple fix for your problem.
Mark & Sheila Heilman & The 3 Fur-Ball Princesses - Nikko, Mai-Thai & Andy
'07 MADP 4523, 2012 GMC Terrain SLT 2 wd
Blue Ox Alladin Tow Bar, M&G Engineering Dinghy Braking System