I NEVER wash a combine in the fall. I rent a BIG portable air compressor and blow it all off. Then in the spring I wash it off and wax it. Even then I really only wash the sheet metal. I do not want any water around any of the moving parts.
Plus I have seen too many washed in the fall and parked in a shed until the next fall. The hydro/shifter cables would be rusted solid and the hydraulic spool valves would stick.