The system was not “USCG Legal” in that it had no functional holding (black water) tank.
Whoever took out the original plumbing replaced it with the head, a Y-Valve and a holding tank that had no pump-out connection.
I’m quite sure that the boat never had a legal holding tank. There is no deck pump out fitting to be found.
If anything had been flushed into the tank, cleaning it out would have required the tank to be removed.
Having read nightmare stories of failed plumbing, issues caused by people flushing toilet paper, macerators that decide to quit macerating and problems finding pump-out stations around the world, I decided to look at alternative methods of human waste disposal.
After a good amount of research, I decided on the Nature’s Head (self contained) Composting toilet.
This toilet has been used in RVs, tiny houses and in boats for a number of years. The concept is that liquid waste and solid waste are separated as they leave the body.
The liquids are stored in a 2.2 gallon tank and the solids are mixed in with peat moss or coconut coir.
The liquid tank can be emptied as needed (ever 3-4 days when used by 2 people) and the solids are emptied ever two months. A constant flow of air is pushed over the solids and vented to the outside.
The vent is not permanent, but allows me to have a functional toilet, so it’s worth it.