Well I'm using 25' right now. Check out the Tetford Sentinel hose.  I am now using one and really like it.. Rhino is what I used to use.
Now: Why support the hose
I have been in a few campgrounds all of which were in the same county where I was advised the LAW (County ordanance) Required a smooth slope to the park sewer inlet.. NO dips. must support hose... Ok no problem have a Slunky.
Fred (RV-101 by Fred) says to use a support to insure the full hose is not dancing around on gravel (THus poking holes in yoru expensive stinky slinky)  Makes sense to me too.