So a few strange things about the black tank on our 1961
1) Placement. It is on the curb (passenger) side while pretty much all dump stations and full hook-ups sites have are on the street (driver's side)
2) It has a 2" outlet hole. This is quite small.
I was able to salvage the Thetford brass attachment plate under the black tank by getting three of the four 1/4"/20 screws out and tapping the fourth for 5/16". I have figured out how to adapt to modern plumbing.
I plan to run a 3" ABS or PVC pipe under the trailer belly pan after coming off the brass plate with a 45 degree elbow (from the exact spot where the original valve was located, just under the tank). In theory, this will increase the (relatively) small fiberglass tank's holding capacity by a few gallons. I will then put the Valterra dump valve on the street side of the trailer, somewhere close behind the tire.
In theory, this would protect the valve a bit, as it is closer to the tire and further front from the bumper and it will have more ground clearance. It will also place the dump valve on the "proper" side of the trailer.
When putting deodorizer in the tank, how will it work with addition of the underbelly pipe? Would I have to sacrifice that capacity anyway by filling the pipe with water until the water reached the bottom of the actual tank to make the deodorizer effective? Or would its sweet smelling power just rise with the contents as it worked its way toward the actual tank?
See diagram. Interesting how I really drew a wide body here. But I think it gets the point across.