Hi, I had a Catalac8m a few years back. Here's what I did:
First the bottom of the
holding tank has to be above the waterline for gravity drain
overboard. You may have to prop up the tank by building a small platform If you only have one 1 and 1/2 inch fitting in the bottom of the tank, run a short hose to a Y valve. One hose after the Y goes to the
thru hull with a sea cock. Use a
Bronze seacock there. The other exit hole of the Y valve goes to a hose that goes up to a
pump out fitting on the deck. If you have two fittings at the bottom of the tank you don't need a Y valve. Just run one hose to the seacock and the other to the pump out fitting. The vent should be connected outside just below the rub rail. The vent hole should be at the top of the tank. Use a
stainless steel fuel tank fitting for the outside. I believe it's a 3/4 inch fitting. The toilet should pump into the top of the tank. Most
tanks are translucent so you should be able to see when it gets full. Get a
stainless steel waste pump out fitting. I think the decks on the catalac are solid but can't remember. Check where the pump out valve will be and make sure there is nothing in the way and it has at least 2 inches clearance all round. Drill a small 1/8 inch hole from underneath and check where it comes out on deck. If it's off a little, don't worry, just drill it again. When you get the right spot, get the correct round hole saw for the fitting that fits on a drill and use the small hole as center. Drill through the deck most of the way. Go inside the boat and drill up to finish. If there is a
core you have to dig out the
core about 3/4 of an inch around the hole and fill with a thickened
epoxy about the consistancy of peanut butter. Let set 24 hours and protect against getting wet. Fit the fitting and drill the three small holes for the fitting. Set the fitting with 5200 and attach the screws from above and the nuts and washers from below. Finger tighten. In a day or so, trim the 5200 from the deck with a sharp knife and tighten up the nuts from underneath. Have someone on deck with a screwdriver so only the nuts will turn. Connect the hose and you're done. Hope this helps, Brad