I have a wagon just like it. It's the drain tube alright. There's a pair: The other one is on the passenger side. You should replace it. Any rubber hose will do. When you operate the A/C, water collects on the evaporator. Lots of water if you live in a hot, humid place. If you have gravity (what's that?) the water will run downhill. As an alternative you can remove all the carpeting and the felt until you have a bare floor. Then you wipe up the water using my special absorbent towels. Looks like Kleenex. I can supply it to you for $500.00 per roll of 20 towels. I'll write "Mercedes" on it.