Hi btbaillie: Pretty certain you could find near-endless entries on the forum on running your black and grey water tanks. danemayer provides a good simple explaination of running proceedure for the tanks. Adding to his comments, I typically run my grey water tanks and black water tank with a closed valve while RVing. As well, after emptying tanks, I add calgon water softener and dawn dish soap to the black water tank. While living in the RV, after 3 to 5 days (depending on use level) I start dumping the black water tank with the black tank flush hooked up and spraying. After that tank is empty (10 minutes or so) with the black tank flush still running, I open each of the 2 grey water tanks to flush the discharge line a bit more. After they are empty, I close the valve on all 3 tanks; and run the black tank flush line for about 5 minutes, adding that 5 gallons of fresh water that danemayer referred to. After shutting the black tank flush line off, I add the calgon and the dawn soap once again to the black water tank.
Now, the bottom line is that I have had no odor since I started using this method. Is this a waste of calgon and dawn soap?....... Maybe; but I have zero tank odor..... And,,,,, on occasion, my tank sensors work. I might add that the sensors don't work very often, but I feel that, when they do, it reinforces my method of tank operation and drainage I use.
Before departure from the RV site, I typically empty the tanks using the previously stated method, and add the calgon and dawn to the black tank, and a little bit of dawn to the grey water tanks to clean some of the buildup that accumulates during its use. The agitation while traveling on to the next site, I feel, cleans some of the phosphate buildup from normal use. As you will see often mentioned, the tank level indicators are near useless and certainly unreliable.
I'm not doing anything new. I've simply taken ideas from people on this forum. Some members use nothing in their tanks. I use my method to eliminate odor that the black tank did have before I started using this softener/soap addition system. Calgon and dawn soap are cheap investments and can be obtained from about any grocery type store. Happy Travels. gebills.