Toilet paper
Your pumpout guy is wrong. The only thing "marine/rv" TP is bad for is your wallet, 'cuz it's just the same cheap flimsy quick dissolve TP you can buy at Sam's, Costco or most supermarkets for 1/4 of the price.
To find out whether any TP is suitable for use in a marine toilet, tear off a sheet and put it in a glass of water...come back in an hour or two and stir the glass. If all you see is some "snow" in milky water, it's the same as "marine/rv"...but if it's still an intact or mostly intact sheet, try another brand.
Avoid all the brands that advertise how strong and soft they are...'cuz they contain extra fibers and creams..a sheet of 'em left in a glass of water for a month will still be intact. Using 'em in a marine toilet is likely to clog a macerating toilet or a macerator pump or plug a tank discharge line.
However, an "overload" of even quick-dissolve TP can clog a toilet pump or head discharge line...but the GOOD news is, it's only temporary...you don't have to take anything apart to clear it. Just leave it alone for an hour or two and the clog will dissolve on its own. But since that could be an major inconvenience, you still need to use it sparingly (5-6 sheets) and instruct your guest to do the same.
And of course, NOTHING should go into a marine toilet that you haven't eaten first except quick-dissolve TP. EVERYTHING else, even a toothpick, needs to go into the trash can.