The top is the under pan of my trailer. The pin that you see is part of the removable tongue. The hole is cut, and I have it attached to a union that was plastic welded into the tank. The left side is the side of my trailer, which terminates at the Bladex valve.
The waste tank only has this one elbow in it. If anything clogs that, and lords knows how anything ever would, because all the sinks have built in mesh drain strainers, I would just unscrew the Bladex valve and run a hose up it. It is also how I can spray down the inside of the tank to remove grime etc. The length of the horizontal pipe is about 10″.
The plastic welding cost about $50 but included the union.
This is the Valterra valve on the side of the trailer. Simple operation, and I can attach a garden hose to it to get some length on draining it if needed.