Why do you need sewer access? Just fill up with water and pump out the pink stuff from the freshwater plumbing. Dump the tanks the first time you go camping.
For future reference: If you learn to winterize using compressed air rather than that stuff, you won't have much of anything to do next time.
Formerly: 2005 Airstream Interstate (Sprinter 2500 T1N)
Now!: 2014 Great West Vans Legend SE (Sprinter 3500 NCV3 I4)