My '77 31' Excella has a rear bath configuration with a rear outside compartment. The blackwater (toilet) valve is visible on the left hand side and the greywater valve is on the right hand side. You will see what looks like a black wooden dowel on top of a metal rod. There may be wire loops which fit snugly over each end of the dowel looking handle. They are there to prevent the valve from opening while you are traveling. The idea is to hook up a fitting to the exterior valve fitting, slip a sewer hose over the end, attach a sewer fitting to the opposite end and screw this into the dump station sewer fitting. Pull the blackwater valve first then close it when it has finished dumping. Pull the greywater valve and allow this to flush sewage from the system. It is now time to fill the tanks again and do your final flush. Hope this helps.
'01 2500hd ext. cab, 8.1 litre gas, 5 sp. Allison auto
3.73 rear end
Mag-Hytec rear diff cover
Amsoil Dual by-pass oil filtration system
Amsoil synthetics all around
265 watt AM Solar, Inc. system