Our manuel toilet in the forward head flushes well but after returning some time later the bowl is 1/4 full of waste. Any suggestions? Its a new toilet used for #1 only.

Suggest you go back to the list of discussions and look at two:
No sea water to either head, and
More stink

Maybe that will give give you some ideas and things to check.

With the limited amount of input you have provided, I can think of three possibilities, but if the unit is new, lets forget about the third:
1.) the vent to the waste tank is clogged and the backpressure created during the pumping process is causing the joker valve or top valve gasket to fail
2.) when you finish flushing (wet) are you moving the switch to (dry) and pumping it dry and leaving the switch in the dry position?
3.) the one I said to forget, since the unit is new, is a failure of the joker valve or top head gasket.

That's all I can think of.

May the flush be with you!!!

Midnightsun171