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RV Doctor: Can an RV be dumped into a home septic system?

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Dear RV Doctor,
We recently got a motorhome from our dad. We just moved and don’t have a place to dump the sewage from the holding tanks. Can we put it into the septic tank of our house? We have been using a blue liquid in the tank, but there is no label on it to tell us what it is, but I assume that this would not be good to put in the septic tank. If we can dump, what should we be putting in the tank that will allow us to dump into the septic tank and also keep the smell down? –- Lisa Vignerot

Dear Lisa,
It is permissible to evacuate the RV holding tanks directly into any three-inch inlet to a septic system as long as your tanks do not contain harmful chemicals such as formaldehyde. Some blue liquid chemicals in fact do contain formaldehyde so your concern is well taken. Until you can verify that the “blue” additive you have been using does not, I would avoid any connection into the septic system. In some locations the practice of dumping RV tanks containing formaldehyde is banned altogether.

Rather than masking odors from the holding tanks with chemicals, I recommend using a biological additive, one that employs live bacteria to literally eliminate the odor-causing molecules themselves. Many suppliers have now produced such an enzyme-based additive. You’ll find a large selection at any well-stocked RV supply center. Avoid using any chemical in the holding tanks, especially those that contain the aforementioned formaldehyde. Additionally, household detergents and some ammonia products may damage seals in the termination valves, so stay away from those as well.

Contrary to what even I have expounded in the past, also avoid home brews. Stick with the commercial brands common to the RV industry. Realize suppliers spend lots of money on R&D, so why risk the integrity of the RV waste system or the eco-balance of a septic system for the sake of a few dollars. Once you switch over to the live “bugs,” use of other types of deodorants and/or detergents will simply kill the good bacteria and defeat the purpose.

As for evacuating the tanks, many RVers completely close the black water tank and evacuate when it approaches full capacity while leaving the gray water valve fully open so bath and kitchen water freely drains the entire time. The drawback to this method is that obnoxious odors can and will proliferate and emanate from the gray tank quite rapidly. I support the method of keeping both container valves fully closed and evacuating each (black tank first, then the gray), when almost full and using the live bacteria additive in each tank. This will also help eliminate erratic monitor panel readings

Gary Bunzer, The RV Doctor is a well known RV author and the host of RV Roadtrips, the DIY Network cable television show. He is one of the RV industry's most sought after speakers and the host of the popular DVD Do It Yourself RV Care.

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