Hi Stosh,
You'll have a fresh water tank drain hose/valve that's probably located on the off-door side just in front of the axles. If you have a washing machine, you probably also have an overflow drain hose.
Low point drains were eliminated from Bighorns and most other models some years ago because of icing problems that could occur in cold weather. The water in the hose that sits between the coroplast and the drain valve freezes when temps drop. The ice can then wick up into the tee, blocking the water flow. If using your rig in sub freezing weather, you'll need to insulate and/or heat the fresh tank drain.