The head on our 278 Vista had never been used by the previous owner until we bought it. Seriously. Its a 1997.
We dont use the "wet flush" option. Instead, I use water from the shower (fresh clean water) to flush the head. However, when we pump the head it takes away the waste but it flushes the bowl with the same water/stuff its taking away

and then the bowl fills itself back up with whatever you flushed away earlier, over an hour period of time. I find myself constantly being reminded of what was flushed away earlier (major yuckage) and constantly pumping the handle on the head to clear it out again. Ive tried the wet flush option, where it takes lake water from the seacock and no difference in operation. Actually, with all of the water, it makes it worse.
I figure the seals or whatever dried out from 15 years of non use. I put some of that marine head lube in there with no difference. Where do I start to fix this problem?