There are three access ports under the saloon floor. These provide access to very large areas of the tanks and are very deep. The hull is one wall of the tank and so whatever the outside water temperature is so will the water in the tank be which can be quite cold to reach down into!
The pedistal for the table is bolted through the top of the tank and so these bolts have to be carefully sealed to avoid leaks.
Here are the two cleanouts under the Port Settee just forward of the navigation station. These also opened reasonably easy. The piece of wood with a piece of teak screwed to it is the tool for opening the old style tank lids. The new style is much easier to work with. Any time a lid becomes damaged I will be replacing them with the new style or anywhere that access is sufficiently difficult that the new style handle improves things significantly.
The last cleanout for this tank is under the drawers in the navigation station. I have not managed to get this one open yet.
When I re-installed the cleanout lids I used plumbers silicone grease on the fiberglass bevil, the threads, the threads of the lid, the o-ring contact points on the lid and the o-ring itself. No issues with any kinds of leaks and the lids open relatively easily!
The cleaning took two weekends to get this tank really clean! My arm is still sore!