I can't speak to your specific unit, but the first step is to crawl under your TT and look for the tank. If you do NOT have a covered underbelly, it should be easy to find. Look for a drain plug or drain valve on the bottom or side of the tank. My Roo and my Mini Lite both came with plugs. I had to add a valve myself.
If you unit has a covered underbelly, look for a drain hose. You may actually have two hoses, one for the drain and one for the vent.
You won't have a drain valve "inside" the TT unless your FW tank is mounted above the frame, which I doubt is the case.
1988 Coleman Sequoia - popup (1987-2009) - outlasted 3 Dodge Grand Caravans!
2012 Roo19 - hybrid (2012-2015)
2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado 1500 Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10