It all depends on how it was winterized. I had an '89 Jamboree and you could blow it out with an air compressor and just put some pink stuff in the traps. Pink stuff is the RV antifreeze for winterizing water systems in RVs. The other option is to use a lot of pink stuff and almost fill the water system with it. My '76 Fireball had this done when I bought it. You will probably have to put the plug back in the water heater. There should be a valve to drain the fresh water tank that may need closing. After that add water and start running water through the system. It may take a few minutes to get water to all the faucets and the air out. After a good flushing you are ready to use it. Since this is your first time with it I would recommend flushing the whole water system. Use some bleach in the water to sanitize it. Personally I carry bottled water for drinking and use the MH water for showers cooking, etc.