RV fridge drain tube should #1 have a plug in the end of the hose, believe it or not but that is a check valve. To let drain water out and to restrict the flow of air back into the fridge. Keeps condensation from forming and iceing up the inside of the fridge.
#2 The hose should have a slight upward bend to it. It would look much like a "P-Trap" much like the under sink trap in the kitchen and bath sink. This helps the flow and keeps the hose clean. Knitters out. This info came from an RV fridge rebuilder and Dometic Inc.