[Motor31]

The black tank is a holding tank. not a sewage treatment center. The chemicals that break down solids usually take longer than the material will stay in the tank. They also may not be kind to your valve seals. The chemicals that some RVers use also may end up "killing" the sewage treatment facility that the park uses. Someone used a boat load of chemicals at one of our favorite RV parks and killed the "bugs" that did treat the sewage in the treatment plant. That left he park with a severe odor problem until the chemicals were finally flushed from the system. Previously there had been no odor problem there.

We dump once a week as that is how long it takes us to fill it. We have gone as long as 9 days but that is chancy as the gauge reads full due to gunk fouling the internal probes in only 3 days. The better probes are the external ones that do not get coated with the contents of the tank. Of course they are more expensive so they were not put in the rigs.

The only time we have had trouble dumping the tank was when the seal on the black tank valve let the liquid drain leaving the solids during the week. Adding a bunch of water let it drain and we replaced the valve. The spray cleaning jet built into the system does an adequate job of flushing remaining solids from the tank after the liquid is gone. Remember that "stuff" floats and is not carried out by the first dump of the tank. You have to rinse it to get it clean. We also put in about 5 gallons of water in the tank when done.

We do 2 loads of wash to get plenty of grey water for hose flushing when stationary. If we are moving a last load the day before and a couple showers are enough to flush the hose the day we leave.

We use no chemicals and no additives in the tank and do not have an odor problem. We do occasionally dump a cup of apple vinegar down the bathroom and kitchen sink to keep the "P" trap fresh.

We're fulltimers so the tanks are never out of use.