V/Flush can only clog if not flushed correctly
And 99% of users don't flush them correctly--they make 2 mistakes: they just "pop" the pedal, releasing it as soon as the bowl is empty, and they ease the pedal back up. The flush pedel not only opens the dome in the bottom of the bowl, releasing the vacuum, it's also the "faucet" that starts the flush water needed to rinse out the bits of solids and paper in the hoses and especially around the bellows in the vacuum pump that can build up and create a clog. The V/Flush can be used with as little as a pint of water...not none at all...so the pedal MUST be left down for 3-5 seconds to put enough water through the system. And if any paper is used, about a cup of water should be brought into the bowl before use (stick your toe under the pedal to do this). Then the pedal should be allowed to snap back up...don't ease it up--let it go!...it's spring-loaded for a reason: to allow the dome to fully re-seat in place. And do not use premium brand toilet paper in it! Use only "marine/rv"...or save money by buying the cheapest, made-from-recycled, institutional grade toilet paper at your local supermarket...it's the same thing as "marine/rv" toilet paper for half the price. If you're in any doubt about whether a toilet paper is suitable for use aboard, tear off a sheet and put it in a glass of water overnight...if it's still a whole sheet, or mostly a whole sheet, in the morning, it'll choke a marine toilet....but if you stir or shake the glass and all the paper has turned to "snow," it's just fine for use aboard.