Like MegaJohn, I use the vinyl fence post. I mounted it on top of my existing bumper. Actually, I just strapped it to the bumper so I didn't have to drill any holes. Holds all my hoses, and the 90* fitting. Used fence caps on both ends. Drilled holes for any water to run out and put hinges and thumb screw on access end.
On my new TT, I glued a 4" sewer cleanout to a closet (toilet) flange, painted it black, and bolted it to the backside of the crosswise frame member at the back of the A frame outboard of the I-beam. I just screw the thing into it. When I get the trailer back from the dealer so I can take some pictures, you will see this mod in the DIY forum.
Note: I am using the Valterra sewer adapter. The angled portion has the threads. The hose has no angle on it at all. The hose is like an extension hose that way, and I can hook as many of them together as I want in any order and only have one 90 degree angle (the sewer adapter). I could set up a 100' dump hose if I wanted! BTW: I am using the Valterra Viper hose. It is not like a slinky -- where you compress it and it immediately uncompresses on you. With it and the Camco Rhino-Flex, when you compress them, they stay compressed. Kind of reminds me of the straws with the accordian bend setup in them.