To be 'safe', measure the longest distance from your camper discharge pipe to the end of your camper and add 10 feet. That way, no matter where the campground dump pipe is located, you can reach it because sometimes, they are NOT where you would expect them. I suggest get the length in 10 foot sections. Then use only 1 section (if don't need to use the entire length). When one smaller section gets pin holes from dragging on the ground, you're only replacing a small section, not everything.
FYI, I carry about 50 feet all the time. With the camping we do, you just never know where that drain is going to be positioned! We very seldom go back to the same place twice. There are just way to many campgrounds and parks to visit in the U.S. of A.! (We live in a great country!)