A/C drain question

On our 78 25ft Argosy the air conditioner is a ColemanMach 3 rotary 13,500 btu with heat.The book for the A/C is dated 10-79 so it probably came out of the factory without A/C. Who ever installed it did not connect it to the condensate drain tube,i have determined that the tube is there and runs up close to the A/C but is not connected! There does not appear to be anything to connect it too, the condensate runs out on the roof and down the outside of the body and does not leak into the trailer.Can anyone tell me how they are usually connected? Was there a special install kit? is such a thing still available? Any suggestions would be greatly appreciated! Don