During the RVing season, I simply backwash the gray water into the black tank prior to dumping.
I use the $1.69 method done once a year at the end of our RVing season.
- put one quart of bleach in each tank
- fill each tank with warm water
- open both gate valves, run the sanicon a little and cap off, then top off each tank with more warm water
- let sit for 1.5-2 hours
- drain everything
- repeat with warm water, allow to sit another 1-2 hours (to remove all bleach residue)
The tanks, tank sensors, waste gates, pipes, and sanicon system are all clean and fresh, like new.
I go the extra step and include the toilet, sinks, and shower pan, bleaching them clean at the end of the season.
It sounds like a lot of fuss, but it really is not. I have been doing this for 14 years. So far so good.