A vent used as a drain is no longer a vent! If you did find a place where you could put it, it would need a trap to keep sewer gasses from escaping. You'd want to ensure the trap didn't dry out when you weren't using the furnace, or it would dry out and start to smell.
I'd consider a condensate pump. Now, where to dump it becomes an issue. A condensate pump can be purchased with various head capabilities, so you could pump it up a ways, maybe into a dishwasher type connection into an existing drain - maybe in the kitchen. Not sure about the code requirements.