That is a very good question. If you find yours, please post the location.
I have a Coleman CTU297RE. The only drains I can find is the low point drains at the rear of the unit. I asked the service tech at Camping World. He has no idea but said that he would check with the factory. No answer yet. Fact is, they have had the unit for warranty service since early October. That's fine though as its been below zero wind chills here for the past several weeks with snow every few days. Can't use it anyway. Ha, Ha.
The Coleman product line has changed hands, at least for customer service, several times since I bought it last May. Camping World is confused because they have submitted the same claims 3 times and they keep getting lost in the shuffles.
The good news is the latest takeover is by Keystone and they seem willing to help.
I will post when I find out anything.