[frank.koetter]

What a project. Thanks for documenting and posting this. I have a 1995 model and have read about the holding tank failure issues. I’m very interested if you believe yours was a corrosion problem or seam issue. In my opinion, I believe the problem could be with the venting. I have investigated mine extensively and concluded that even with a brand new vent filter the air can’t flow back into the tank at the same rate as the waste that is being removed. This scenario results with the aluminum holding tank pulling in on itself creating a loud bass drum sound. My guess is that an aluminum holding tank can only tolerate this so many times before it finally fails. I experience the same sound when the main VacuFlush head is used more than once within a minute or two. The extra air pushing into the tank can’t flow through the vent fast enough and pushes the tank sides out resulting with the same bass drum sound.

A good solution that worked for me was adding a “T” with a cap within the vent line between the holding tank and the vent filter. Simply remove the cap anytime you’re pumping out and allow unobstructed air into the tank. This solved the issue for me….but educating my guests about the double flush is still required.

I appreciate your information and the solution.  I have a similar problem during pump outs.  I've just added a new style holding tank vent filter.  It's called...Big Orange OEM holding tank vent filter. It has a vent in it to do what you've done.  I wasn't able to add a picture, but it's worth googling the name so you can see it.  This might be the solution for you.