I have a 63 Globetrotter. You can get some idea of how the black tank is
situated in this model by looking at
http://www.nwflorida.net/gt00004.htm
This page details the time I took the black tank out and repaired the
floor around it.
Basically the black tank sits on top of the floor inside a wooden "box"
with the toilet mounted on top of the box and tank. Note the tank is
shaped to fit the curve of the rear of the coach.
The drain is directly below the top hole. Their are two shots of the
bottom of the tank with one showing how the valve is mounted to the tank.
Not shown ( and I don't have a picture) is the 4 way PVC connector that
mounts underneath the valve. It is like a cross with the top connected
to the valve , the bottom is what goes thru the belly pan and has the
connector to hook your sewer hose. The two side connections allow the
gray water from the sink and the tub/bath sink to drain into the same
sewer hose. Note the gray water enters the cross pipe below the black
tank. You can see the gray water pipes in the third picture down on the
left side. These pipes had rubber sleeves and clamps rather than being
cemented together. I tried to find this connector at my local RV parts
shops but failed so I repaired and reused my old connector. The black
tank is made from fiberglass and was in good shape.