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Harvey,
The records show that only the newly introduced 1973 Excella 500 had a gray tank. Starting in 1974 all models had them. Some of the early rear bath designs had some pretty convoluted arrangements of tanks and valves. Tank capacities were pretty small. These problems were one of the prime drivers for moving the bath forward in the coach. All Airstream's came with a single drain water outlet. A coach with a black tank only had only one valve with the gray water passing by in a 3 inch Y going to the outlet. Valve locations were pretty obvious being at the back, side or bottom of the one tank, usually pretty close to the toilet. With introduction of the gray tank the plumbing and valve locations went every where. One word of caution for folks with older coaches with the single black tank valve that comes up at a 45 deg angle from the back center of the tank. That angled pipe/valve mount fitting is no longer available. While the valve can be replaced, you must not cut the old fitting to get to it. To do so will require a serious replumbing job. Can't tell you how many times someone has come in with part of the fitting expecting to find a new one. ("They're common parts, aren't they?") Charlie |