360exp holding tank

The Sealand black water holding tank on our 360 has blown out its tanksaver valve while offshore in the GOM twice in the past month. The valve is the device set in the top-rear of the holding tank that is supposed to vent air into the tank during vacuum pump outs to protect the tank from imploding. Well that's just great but what about protecting the rest of the boat from the effluent when the valve comes out and the stuff sloshes all over the starboard wing compartment and into the bilge stinking up the whole boat. The 1.5 inch diameter check valve sits in a 2 inch grommet that goes into a hole in the top of the tank. Both are friction fit devices with no threads or set screws to hold in place.

The tank was only half full both times and the sloshing in the tank obviously forced the valve out. After the first time I squeezed into the compartment and replaced the valve, which was no simple trick considering my size and the rest of the hardware in that space.

Now I have to remove the facade wall on the starboard side of the aft berth and cut out more of the bulkhead, remove the six steering and throttle actuators and associated hoses and cables to the Yami outboards and various other electronic modules before even getting to the holding tank and all of its piping and wiring so I can get it out of the boat, power wash it and wash out the compartment and the bilges all the way to the stern. And then reassemble the whole thing again.

Sorry I got carried away. The local repair guys say this happens all the time with holding tanks. So when I reinstall another tanksaver valve - which Sealand promotes as a plus for not having any threads! - after cleaning the whole thing and replacing the duckbill valves and tanks level sensors since it will be out of the boat, has anyone tried gluing the valve into the grommet and then screwing the grommet to the tank top to keep it in place? I do not want to do this job twice! Actually, now I am thinking about finding a way to patch that 2 inch hole and drilling a new hole in the front top of the tank for the valve so that it is easier to reach and perhaps not subject to as much sloshing force.

I definitely will not run in anything bigger than calm water with anything in that damn tank again. It is a poor design by Dometic/Sealand and poor layout by GW for putting the tank in such a way that the valve is on the backend.

Yes, it was properly installed. The grommet fits in the tank hole and the valve fits in the grommet. They were both seated properly. Tight fit too, but there is nothing but friction holding both in. The grommet stayed in the hole both times and the valve popped out. I think I actually heard it pop out last week as I was in the cabin while underway in 2-3 foot seas at 25 knots and heard a distinct crack-pop sound. I even remarked to the other fellow in the cabin "what the hell was that." But there was no indication of trouble at the time on the electric panel or the console so I let it go.

It is quite possible that the valve had been out of the tank for quite awhile. We bought the boat three months ago and the original owner had complained about an odor in the boat more than a year ago. His solution at the time was to keep the holding tank as empty as possible. It was not until our first offshore trip and the terrible odor that I started to investigate and found the valve missing the first time.

I want to add closure to this holding tank issue with help from the Sealand folks and their rep at AER Supply in Seabrook TX.

The issue turned out to be a combination of stuck sensors on the tank level indicator so that the tank was near full or full when it only read low or mid full and the tank saver valve and vent location. The tank valve saver and the vent line are both on top at the aft end of the tank. When the boat is on plane the liquid in the full or nearly full tank shifts aft and gets flush with the top of the tank in the back. This blocks the vent line. With the level indicators malfunctioning the head does not shut down and so continued use causes more liquids to fill the vapor space in the tank and pressurizes the tank. The weakest link is the the tank saver valve that is installed with only a friction fit and so it pops out.

I took the whole tank assembly and pumps out and pressure washed them and installed new level indicators. I plugged the existing vent line hole and drilled a new one in the only available space which is about six inches from the front of the tank on top and ran a new hose to the thru hull. I also strapped down the tank saver valve with a piece of SS strap by screwing it into the top of the tank across the top of the valve. I sanitized the whole compartment and washed the bilge with tons of freshwater and reinstalled all the parts and systems that had to be removed to get access. Only had two screws left over that I left out of something!

Now the boat smells fine and the head system works fine. I checked another 360 owner in our marina and his tank saver valve was blown out too.

I had checked the vent and it was open. The screen was already removed or broken through because I pushed a flexible tie wrap in one end and pulled it out the other end. I would post photos of the project but I cannot figure out how. I checked the FAQs but did not see any references to photos.