Clear Sewer Adapter w/Tank Flush Adapter - Which One???

I purchased all the materials needed from Lowes - except the orange swivel fittings (2) that I use with my regular sewer hose. Don't remember the exact names or sizes but it was not hard to pick them out. Goes together very easily and comes apart when you need to move the trailer for any reason.

Edit: Forgot one of your requirements. This Flush King would attach to the 2nd orange colored clear angle in my pictures below. It will swivel to any angle you wish and, along with the other orange clear angle fittings, allows the long drain tube to be raised up and/or rotated outwards as much as you need to reach the drain hole.
This is also possible with the pictured fittings.

I have used the Flush King many times and find it does a fair job of rinsing out the tank but the best way to clean your tank still remains the good old "down the toilet" wand.
Barney

Lots to choose from.

Clear bayonet and bayonet swivel style RV sewer fittings

3 inch fernco pipe coupling

3 inch tank back flush fittings

I had a 90 degree hydroflush with 6 feet (unstretched) of standard heavy mil Camco RV sewer hose connected to my house clean out for 4 years. The cleanout was about 3 feet under the trailer. The vertical run of hose had full shade and the horizontal run was supported by a piece of vinyl gutter and covered with another piece of gutter. It is still in great shape. As long as the hose is good quality and not exposed to direct sunlight it should last a very long time.

What you want is this rotating sewer adapter that will convert a standard RV 3" sewer outlet so you can then buy whatever else you need to complete the connection to the sewer inlet using standard plumbing parts from Home Depot, etc. Any other RV fitting such as a clear section or back flusher such as a Flush King can be connected to the trailer with this swivel fitting then connecting to it.