[prairieschooner]

I just had another thought but no sure how or where to pull it off. On boats we go to a pump-out station. There is a large diaphragm pump that creates a vacuum and pulls the waste out.
Here is a link to a product that I discussed last year during a previous discussion, the Sewer Solution; http://www.sewersolution.com/
This is a cap that would attach to the discharge fitting although you may also need an adapter. The cap has a water hose fitting and the jet spray is able to go into the tank or help discharge the waste. I would really think hard about this product to help with you dilemma and it would be much less than paying a shop to work on it, if it didn't work at least it would be a piece of gear. The people that purchase this at the RV park that we were at swore by it.