From the 40TD plumbing diagrams I see 2 gray tanks. One is 67 gal. and the washer and shower go to this tank.
The bathroom sink and toilet go to the 52 gal. black tank.
The kitchen sink goes to the 2nd gray tank. I can't find the size of this tank on the diagrams but the 40TD specs show 117 gal. gray capacity. 117-67=50 so the kitchen gray tank must be ~50 gal.
Each of the 3 tanks has it's own vent to the roof and own dump valve.
3 cheers for Winnebago for placing diagrams on the internet. I know of no other manufacturer that does this.
Sarver, PA/Crystal River, FL/Shelocta, PA · FMCA 335149 · W3TLN
2005 Suncruiser 38R · W24, no chassis mods needed · 2013 Honda Accord EX-L · 2008 Honda Odyssey EX-L