Re: Holding tank -- sewage, etc.
What you have is a 3" pipe sticking out, with bayonet lugs, and 1 valve (which slides open) for each tank. Usually 1 gray for sinks and shower and 1 black for the toilet. The dump station will be a pipe in the ground. So, you need a leakproof connection from that 3" pipe on the RV to the pipe in the ground (which may be any of many sizes).
To transport the stuff from the trailer to the dump site, you will need a hose. Usually 10' is enough, but it is good to have a second 10' section just in case the site layout is really strange. You want the very best hose you can get, as the thinner the hose material, the sooner it will leak 'stuff' over you and over the ground. If you got a hose 'free' with the trailer, it will probably be the crappiest available
My favorite at the moment is the 'Rhino' hose. The 'blue' press fit system is not bad, and they have a new extra heavy duty hose which seems good.
Next, you need to connect one end of the hose to your trailer. If the hose has a connector on the end, fine, otherwise you will need to get one and attach it to the hose. Then just press it on the pipe coming out of your trailer, and rotate until the ears of the connector lock on the lugs on the RV pipe. On the other end, you need to connect the hose to the pipe in the ground, which is made more difficult by there being so many different ones. A 'universal' elbow which screw into or fits snugly in most pipes is a good choice. Again, you may need to get a connector to attach the hose to the elbow. The 'blue' press fit universal elbow seems the most versatile, the Rhino elbow is not bad, and there is a new 'red' elbow which looks like it might be fairly good. If you have a second chunk of hose, make sure you have any connectors needed to connect the 2 hoses together.
This is the minimum you need. The next step up is to insert a section of clear pipe between your RV and the hose. These can be 90 degree angles, 45 degree angles, or a straight pipe, depending on your layout. There are also ones which have a water hose connection which allows you to 'backflush' the tanks.
To use a backflusher, hook up the sewer system, and hook a water hose to the backflusher. This must NOT be a drinking water hose, so a color other than white is best. (and don't use any color hose for drinking water except white, drinking water certified hoses, as most 'garden' hoses are made with harmful chemicals) And it MUST have an anti-backflow valve to keep the crap (literally) from getting back into the drinking water. Plastic is cheap, but breaks easily. So I have a plastic one on the flusher end and a good brass one on the other end of the hose. Yes, I am anal.
To flush, make sure both the gray and black tanks are at least 1/2 full. Open the valve for the black tank and watch in horrid facination at the stuff coming through that clear section of pipe. When the flow stops, turn on the water into the backflusher for a period of time which you figure out by trial and error. 90 seconds seems to work for me, just make sure that your tank does not fill more than say 1/4. Let it drain out. Repeat until what comes out is clear and has minimal 'chunks' in it. Close the black valve and open the gray valve. This will rinse out the system and your hose. You can backflush the gray tank, but it is not as important as it is with the black tank.
If you want to use some other flushing system than the backflusher, let me know and I will provide some guidance. You can get by without any backflushing, but your tanks will not be their cleanest.