Where did you read that Raritan requires you to do that?
Any toilet--in fact, most equipment--will perform more efficiently and have a longer lifespan if it gets recommended preventive maintenance. But whether you choose do it or not is entirely up to you.
Sea water wouldn't even be coming in when the toilet is set to "wet" unless you're pumping it. It's coming in because there's no vented loop in the intake. It needs to be installed between the pump and the bowl and be at least 6-8" above waterline at ANY angle of heel, not just when the boat is at rest....which, on most boats, puts it 2-3' above the bowl (see photo...small one is the intake loop, the large one is in the discharge line, usually only needed if the toilet is plumbed to flush directly overboard at sea). It's there to protect your boat if the pump is left in the wet mode or parts fail...or the intake seacock is let open while away from the boat.
-- Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein