You don't mention the coach or type of RV you have however this is a common problem. A few things you can try.
First use a good formaldehyde based chemical (the blue stuff).
Second use any powered water softener and laundry detergent
Here is the procedure:
After dumping fill the toilet bowl full with just water and flush
Fill the bowl again with water add water softener, chemicals and detergent and flush again
What this will do is fill the plumbing from the gate valve to the tank with water and then the bottom of the tank with water and chemical before you flush any solids. The water softener will keep the walls of your take slippery and the detergent will keep them clean and break up the waste. The formaldehyde will keep the odor down.
Next: when using the toilet for solids fill the bowl 3/4 full prior to use. After use immediately flush not more than 1' of toilet paper and refill with water again. Do not fill the bowl more than about 2' of toilet paper per flush. This will provide adiquate water to move the toilet paper. Do not empty the tank until it is 3/4 full or more. If you have a flush system by all means use it every time you can.
If this doesn't work there are other options that cost money but will nearly eliminiate the problem.