You rang???
First, if you're certain your toilet is a Jabsco, there's only one manual Jabsco toilet. And this is the owners manual for it
Jabsco Manual Twist & Lock owners manual However, electric toilets aren't uncommon on a 31' boat...if that's what yours is, I'll need the model # to know which one so I can give you the link to the manual for it.
If you're 100% certain that what you're seeing is runback from the tank, and if it only happens when you're heeled far enough, here's what's happening: When you're heeled, even a half full tank can spill into the toilet discharge line and run back to the toilet (also out the vent line which can cause other problems)... Where, in the discharge fitting you'll find a rubber one-way valve called the joker valve (I don't know why either)...it's a cup-shaped doodad with a slit in the bottom and "lips" on the outside of the bottom. (part #34 in the exploded drawing in the manual) A brand new one will block run back for a short while, but as flushes go through it, over time the slit and lips become stretched...at first it just allows slow seepage, but as the slit gets wider it allows more and more....until finally it's no longer a slit it's just a hole. So replacing the joker valve is the short term fix...but that's ok, 'cuz joker valves should be replaced at least annually anyway. There is a more or less permanent fix, but it requires completely rerouting the discharge line and you still should replace the joker valve every year.
You've made it pretty obvious that you don't have a clue how your toilet or anything else in a sanitation system works...but that's ok, none of us were born knowing anything about ANYthing. Which is why I've written a couple of books...you'll find a link to the current edition in my signature below.
The title (my publisher's idea) is a bit misleading...'cuz although it does deal with every source of odor on a boat and how to cure, or better yet PREVENT 'em, it's actually a comprehensive "marine toilets and sanitation systems 101" manual that explains the laws, describes all the types of systems and how they work, and will help you learn how to operate and maintain your system to prevent 99% of problems instead of having to cure 'em. 'Cuz you get to do any preventive maintenance on your terms when it's convenient...the need to cure a problem never happens when it is! And I'm always glad to answer any questions it doesn't.
--Peggie