It might not be a valid comparison, but I just found the drain on my 02 Georgetown (we've had it 12 months now). Under the bedroom wardrobes is an area that is blocked off when the bedroom slide is closed. There are two cupboard doors down there that are placarded "Not for Storage" and couldn't be opened.
While trouble-shooting a problem with the TV cable hook-up, I took a closer look at those doors and found they were held closed by woodscrews through the door into the frame. After taking the screws out, I found that the doors wer openable and that the electrical distribution system is in one half of the cabinet and the potable water tank occupies the other half.
Surprise - there's a hand valve on the potable plumbing that drains the tank! Prior to finding this, I was running the water pump through the kitchen sink faucets until it quit pumping, then I'd drive to our nearby dump station to empty the tank.
Because we have such good quality city water at home (one of the top 5 nationally) we like to take a full tank with us. Occasionally we've had to supplement with camground water just to cover the requirements for last night out or the trip home.
We've picked up some pretty scuzzy stuff! Now I know how to dump that stuff for a high quality refill.
Frank and Eileen
No longer RVers or FR owners