DH here, everything from the project came from Home Depot, 4 inch pipe, used the black glue as well so I didn't end up with purple streaks on the project. I did have to use my Dremel tool to grind off 'some' the sides of the bayonet fitting on the sewer hose, other wise it wouldn't make it through the pipe. Nice thing with the 60 degree neck on the end is keeps the end of the hose there rather than sliding in to the pipe should I not have the spare hose at the end. It is large enough to hold two hoses and the hose connector - 4 inch pipe I cut to 6 1/2 feet (don't ask me metric), I had more room I could have made it longer, but wanted to easily be able to pull hose from the other end without busting my knuckles on the landing gear. I do need to lengthen the chains by about 6 inches (right now each one is a 12 inches), has a tendency to bunch up on turning the ends, even with a slightly loose screw on them, self tapping screw here (5/8 inch) on both sides of the chain. Just make sure if you do project, you don't drill the threads the pipe goes into. Also put hose clamps on before I glued the ends. Drilled air holes on top every 10 inches - 3/4 inch bit I believe, and then two on the bottom for drain of any water at both ends.
One small correction, I did not drill the frame of the trailer, just the triangular shaped metal pieces that attach to the frame and that connect to the side of the trailer (don't ask me what they are called), picky I know, but in my mind the frame is what the body of the trailer is setting on similar to the frame on my truck - last thing I wanted to do was drill a hole there. I used a caliper to ensure all measurements were the same once I figured out where the first bracket went and just copied the dimensions to the next two brackets. Original boom configuration was in this area, so I know the area is strong to cover the weight of the entire thing plus the total weight is distributed over three points for the entire distance of the pipe so I should be fine there.
Of course it took two pairs of hands to hold it up there first, so thank heavens Renee helped position it properly.
ID Number on the bracket (hanger) if you can't tell from the picture: SIMPSON Strong-Tie A21 ESR-2523. I actually got different ones trying to figure this out, but this is the one that worked for me. Not a lot of vertical height on my configuration for the attachment so I had to go with a short side on the connection to the trailer.
Oh and just to give credit to someone, not sure who, did do some research on-line before doing the project, saw a similar sewer hose storage arrangement and just copied the idea, I think his was white, I wanted something that would disappear into the trailer if you weren't looking for it.