We use a Lavac head, which we’ve found to be trouble free.  The Lavac head uses a standard Henderson diaphragm pump.  We added some PVC plumbing and valves on the input side of the diaphragm pump so that we can also use it as a backup bilge pump, to pump out the floor of the head if we use the hand-shower, or to empty the holding tank.

The head sink is tee’d into the intake plumbing of the Lavac head, so drains into the head.

The saltwater intake for the Lavac head is plumbed into one of the cockpit scuppers, thus eliminating a thru hull.