Gary, is there a clamp on the 310? I browsed the owners manual and didn't see where the upper and lower sections come apart. I've had our 210 apart and there is a clamp but not sure about the 310.In general tightening the hose clamp might help but sometimes it does not and the leak gets worse. It might be best to buy a replacement rubber seal then take it apart, clean everything and put the new seal in.
It it is fairly easy fix if you can be on your knees for a while.
But remember my first comment.....tighter is not always better!
Vacuum breaker is dry it around crease. If I run my hand around the crease or a towel. Water comes out heavy. Apparently this section is factory sealed and I guess this is problem. I know Dometic has a 2year and a 10year warranty. Its a 2011 fifth wheel bought in 2012.
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Update. I called Dometic and they overnighted me a new 310 toilet.
Awesome customer service
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Since you will be putting in a new toilet it will be a good time to put in a in line water shut off valve for the toilet.
Don