Our hoses need to be replaced. I have a gallon bottle of liquid deodorizer (dry stuff mixed with water) standing by and pour some in the bowel every time I flush near the end leaving it in the hoses. Doing that for a week every time it's used seems to help the problem quite a bit. We have Vacuflush which uses fresh water. I don't know if salt water would have the same effect but may.

I do that whether it goes into the tank or directly overboard. If were in an anchorage that demands a tank we've been known to leave it in the bowel, pour some deodorant in and wait till we're on our way before flushing as I don't want to use the tank unless absolutely necessary.