We have a 1982 with all the original paperwork. There was no manual only a few items relating to the appliances.
If you have any specific questions I'm sure the members will be happy to answer them.
There are really four tanks. The freshwater tank under the sink, the black tank under the fridge and toilet accessible from the end of the cabinet and the grey tank located under the floor between the kitchen and bath. The hotwater tank might also be considered a tank since it hold 25% of the fresh water.
There are seperate valves for dumping the grey and black tanks. Generally you dump the black tank first and then the grey tank. The black tank dumps with a woosh since it's higher and due to it's shape, The grey tank dumps slowly since it's a pancake design, wide area and thin.
Dumping the grey tank flushes the hose though it never smells any better than the black tank to me.
We generally get 2-3 days on a grey tank and 5-7 on a black tank though we generally dump them at the same time. We do use Scott toilet tissue which seems to dissolve very well.
Hope this helps a little and enjoy your 1550.
Norm and Ginny Milliard
1982 Sunline 15.5 SB
2004 Honda CRV 4 cyl, manual