One of the more useful tools for boondockers who like to 'hunker down for a spell,' and not move the rig is the "blue boy," or portable waste transport tank. Nothing more than a plastic tank, usually equipped with wheels, one simply hooks their sewer hose to their rig's dump port, the other end to a similar fitting on the blue boy, and discharge your tankage into your rolling receptacle for transfer to a nearby dump station.
Oh, but it were that simple. And for the most part, it is. But there are a few tricks that will make your experiences with using a blue boy a lot easier, and in some cases, less messy.
First, blue boys come in various sizes, and of course, the bigger they are, the bigger the price. The largest of the blue boys typically come equipped with two ports--one at the "top" of the tank, the other on the side. The latter, equipped with a blade valve like the one on your RV, is for dumping. Smaller tanks without this blade valve have to be stood on end to dump. This writer once "stood up" a 15 gallon model and found he had back muscles he wasn't previously familiar with. After obtaining a 20 gallon version with the blade valve, back strains were a thing of the past.
But how do you dump a 40 gallon tank into a 20 gallon blue boy? Start by dumping black water in the tank. Each blue boy is equipped with a small capped opening to release air. Some RVers equip this opening with a "bobber" like device that sends up a flat as the fluid level in the tank rises. Others simply look closely to see the rise in the liquid level through the port. Beware! A fast dump can give you more than just, "Mud in your eye!" Once the first "load" is taken care of, return to the RV, and dump the next load.
At this point, you may find that in practice, some undesirables (solids) are still hanging around in your black water tank like errant Klingons, waiting for the Enterprise. A backflush is in order! If both your gray water and black water tanks share a common discharge port here's the ticket: With the sewer hose disconnected from the blue boy, but still connected to the common dump port, raise the blue boy end of the sewer hose HIGHER than the level of your RV waste tanks. Open the black water valve, leave it open, and quickly open the gray water valve, allowing a rush of gray water to force its way into the black tank. Close the gray water valve, then the black water valve, and with oh so much care, reconnect the dump hose to the blue boy. Now reopen the black water valve and dump the black/gray backflushed liquid into the tank. This should have dislodged the "Klingons."
It's a bit of a trick, and one best done with a medium length hose and an assistant, if one should happen to be available. Usually it take a substantial bribe to get your mate to help you with this one.