I've got a 94 2500 diesel, and my evaporator drain is leaking into the cab on the floorboard. I got under the passenger side of the truck and noticed the metal port coming through the firewall, however, there is no hose to direct it down in front of the firewall. Do you guys know what size hose goes on the port?

 

there is normally no hose.

seal the crack in the firewall around the pipe with black rtv, and poke out any obstruction in the pipe with a wire or wire tie.

if you feel like you need a hose, its about 7/16 - 1/2"

 

I'll confirm 5/8" ID hose fits nicely.