Not sure why "everyone" is telling you not to use the bathroom in your Jayflight. I do not own this type of trailer, but would think it is just as easy as any other Jayco or other brand. Basically, you need to make sure that your black tank is at least 2/3 full before you drain it, so sludge will flow out the drain smoothly and rapidly. In order to do this, don't hook up your drain hose to the trailer and then leave the valves open - keep them closed (both gray water and black water) until they are 2/3 or so full, then open the black valve. Wait until it stops flowing, close the black valve, then open gray valve to rinse out the line. Same applies if you are using a dump station instead of a sewage connection at your site.
If you need to more thoroughly clean the black tank, there are inexpensive water wands available that you can hook up to a hose and push down the toilet past the flush valve, which will then spray water in a rinsing action to dislodge clumps remaining in the tank. There are also flush kits which can be installed in the tank permanently, which allow you to hook up the hose outside the trailer. These also send a rinsing spray into the tank to help clean it.
One last thing that I do is to pour a homemade solution into the tank before every trip, along with a bag of ice cubes and a couple of gallons of water. The sloshing action while towing the trailer to the CG really helps keep the tank clean and odor-free. Solution is: 8 oz of liquid water softener, 8 oz of ammonia, 8 oz of Pine-Sol, and 1 cup of baking soda. Mix these together in a gallon jug, then fill the jug with water and mix again. Pour about a cup down each drain (sink, lavatory, etc) and the rest down the toilet with the ice cubes and water.
You will be surprised how clean and odor-free your tank will be. We have been camping for more years than we can remember, and have never had a hard time keeping our tanks clean.
