I use something along the line of "Holding Tank with Multiple Discharge Options" except I eliminated the "Y valve" selecting the macerator or deck suck out. There is no need for it. A simple "Tee" works. As long as the through hull is closed you can be pumped out. Likewise if the cap is in the deck fitting the pump has suction. Been doing this since about '90 and have helped friends set up the same way. It seems to be an effective way to live within the law and has not received any negative comments from various potty patrols. I also chain and pad lock the overboard discharge.