Originally Posted by vcu70
I have only one T handle valve to dump and it seems I have only one tank for gray and black water on my 77 20' Argosy-Correct?
Your coach was produced in a transition year for 20' Argosy coaches. The Standard Argosy 20 was produced in small numbers while the Argosy Minuet 6.0 Metre production got underway. There are a few differences in the coaches and one of them is in the plumbing. I will answer for the Minuet 6.0 Metre since it is the rig with which I am familiar.
To distinguish between the two coaches one must observe one of two features. In a rig with the front sofa, the presence of a streetside upholstered arm indicates a standard Argosy 20 == no upholstered arm indicates a Minuet 6.0 Metre. The other method is floor width measurement -- 7' indicates a Minuet 6.0 Metre -- 7' 8" indicates a standard Argosy 20.
The first project would be to identify if the coach actually has both of its original waste tanks. The graywater tank was installed on the floor of the rear streetside wardrobe. The blackwater tank was installed on the floor under the toilet and vanity. The original plumbing would have had both dump handles in the rear bumper storage compartment -- placquards were riveted above each of the two handles to denote its function.
It is not uncommon to find serious modification to this wastewater plumbing. The clearance on the Minuet 6.0 Metre is very minimal and it is not uncommon to drag the rear when navigating dips when coping with driveways, etc. Some owners also found the graywater tank to be of more nuisance value than help since it didn't collect the shower's waste water -- the shower waste water exits below the dump valves -- so their solution was to remove the graywater tank and reconfigure the plumbing to resemble that utilized in the years before graywater tanks were mounted. My Minuet had its graywater tank removed, but good fortune smiled upon me as the owner retained it and included it with my purchas -- I just have to get it re-installed.
Good luck with your investigation.