Many store them in the rear bumper, but danger there is that it is just a matter of time before you lose an end cap off the bumper while travelling and get to your destination to find you have lost your hose. As you begin your travels you will undoubtedly spot some sewer hoses scattered along the side of the highway, then you will see what I mean. Many get a tote or Rubbermaid container to store their sewer hose and other sewer tools/accessories, rather than storing in the bumper.
Also never ever leave your black water tank valve open while camped. Let it fill and dump when it is close to full. Otherwise you will get a buildup of solids on the bottom of your tank. You need lots of liquids in your tank to help flush out the solids and break up the solids and paper in the tank. Lots and lots of reading to be had in this forum on the subject if you do a search. You wouldn't believe there could be so much conversation about toilet paper and poop!