I have a 2805C model. It came with a 30 gallon gray water tank. Since we camp several times a year in camprgounds without full hookups I decided to add an additional gray water tank. Just mounted it in the underbay next to the existing gray water tank. Venting was connected to the vent piping under the shower. It is "piggy backed" and fills via the cmper's drain pipe. That was the best place for me to have it filled from. Now as water in introduced into the original gray water tank the water also fills up the new tank. Kind of hard to explain so I have photos should anyone wish to see them. Send me your e-mail and I'll send them on. But I cut the drain line and added a tee to which I piped the new tank. It works but with both tanks having water in them it does drain slower when I dump.
God Bless
Papa

That's exactly what I am planning for mine. Papa I sent you a pm

__________________
2001 GMC Savana
Classic 2693 RD
Luke 1:49

I have looked at the space available for additional water storage between the girders under my 2207T and there is none! The gray water tank on my Hi-Lo is a non-stock item in that it has a channel molded into it to allow the rear cables to pass through to the ram which is located between the axles; so it would be expensive to have a one-of custom tank built in order to hang a larger one in it's place.

__________________
John

2007-22T TowLite 50th Anniversary, Valley Towing Equalizer Hitch
2008 Nissan Frontier SE 4X4 Crew Cab, Snug Top & McKesh Mirrors
Cooper AT3 LT265/70R16 AT w Slotted Rotors, Ride-Rite Air Springs