Up until last weekend at a dog show in Louisville a 15' slinky hose has been all I've needed. We were one of thousands of RVs and had a dedicated spot but the sewer was a good 30' away. Moving was not a option as every single spot was reserved with trailers inbound from all over the country and arriving by the minute.
I went to the local Walmart and bought four 10' sections and now have them when ever I need them again. They each came with clamp on caps for when not in use and a 90° elbow for the sewer connection not that I need three of those.
In the end we can all recommend this length or that but there will be a time when it won't work ;)