I believe the proper term is MSD... I looked in your book Peggie, (thanks again) and did not see any recommended "plumbing drawings."

I thought I had seen drawings here in the past... for recommended systems...

What I want is holding, overboard discharge, and pump out at the deck.

I am willing to forgo direct overboard discharge if there is a suitable method for me to easily empty the tank (in line macerator).

What I have now is a Y valve for overboard/tank, and only a deck pumpout... the latter being a pain to use as I have to find a pumpout station.

I have one vented loop, but I am not sure it is in the right place. I have a hard valve to cut off the incoming seawater to the head, and I close that when I leave the boat.

Is there a recommended book for this... Calder perhaps? (I have other boat systems that no doubt need updating).