Winterizing your RV can be a bit tricky, especially finding those drain valves. The drain valves for your black and grey water tanks are typically located underneath the RV, often near the tank itself. Look for low points in the plumbing lines, and you might find them there.
If you have the owner's manual for your 2014 Thunderbolt XLR toy hauler, that would be a great resource. If not, consider reaching out to the manufacturer's customer support or an RV community/forum for specific guidance. People who own the same model often share valuable insights and tips. Safe travels!