What McGinnis said.
setup is manual head
that pumps through a vented loop, Y valve, and a short line to either the holding tank
or the overboard
discharge. I have a pumpout fitting with a hose and a pipe that picks up through the top of the tank at 1" off the bottom. The vent is 5/8" CLEAR hose to a through-hull about a foot below deck
level, no vented loop. At that height, siphoning seawater into the tank is a pretty remote
possibility and even if it fills up, that just means I can't flush until I pump out. I have no flame screen
. I don't consider it necessary, having never heard of a similar installation
exploding. The nice thing about the plastic vent tubing is I can easily see if it is clogged or might be clogged, and just replace it. This is a handy size tubing and I usually have at least 10-12 feet of it on the boat for fluid transfers, etc.
Eventually I will probably change the setup so I can dump the tank at sea but for now I like having all my fittings at the top of the tank. Even a slow drip of a leak is something to be avoided.