so here it is. The pump selection Y valve chooses to suck either from the toilet bowl or the tank outlet. The chosen contents go over the vented loop to the output selection valve, which choses whether they go to the thru hull or tank. There is a T on the tank outlet with the other branch going to the deck pumpout. To use it, you need to make sure the pump selection valve is set to pump the head, or you cannot get suction on the tank from the deck. Similarly to pump overboard, the cap has to be on the deck pumpout. Also if you happen to pick a particularly bad combination of valve settings, you will just pump the contents of the tank back to the tank - so don't do that. This has all worked well in practice.

This was an early picture (I don't have one of the final deal), several things have been changed: On a Lavac head you should not mount the Henderson pump sideways as shown - it does not work well that way and was turned upright. Also the hose leading from the tank outlet to the T was not supposed to be there, now it has a hard piece of PVC from tank outlet glued into the T. A lot of effort was put into having the least possible amount of hose flooded with effluent because that is the weak point for leaks and odors. Also every place there is hose, efforts were to keep it sloping downhill so that it did not trap effluent. You can see that (excepting the hose to the T) after you are done flushing, there will be no effluent left in any hose in the system.

The box up to the right is actually all of the electronic navigation gear - rather than spread it all over a bulkhead and use a bunch of space, I made them build that little cabinet. The door opens like the leaves of a book, inside on the pages are mounted the autopilot, VHF, Sirius Weather receiver, Ethernet switch, etc. Makes it very tidy compact yet still easy to get to everything. The gage to the left is the original Volvo engine gage, deemed too ugly for sight. Engine data can be read from anywhere in the instrument system, so this gage was stuck there on the theory that when the whole instrument system went down, you could still look there in case you needed to. That is the dual fuel filters way off to the left very comfortable to stand there and change them out if needed, and an easy reach through the hatch.