We purchased a 2003 BT 5270 new and pre-winterized. When we took it to Camping World to get it dewinterized on our way to FL, they could find the drain valves, and, believe it or not, a call to Gulfstream indicated that they didn't have a clue either..CW finally found the three valves in front of the fresh water tank, and the system finally drained. We subsequently had a bypass installed, but it was a PITA to access it as we had to remove the mattress and part of the plywood underlayment to get to it through an access panel we had to cut.
We loved the BT for a number of reasons - but the drain valves were not one reason.
Sold the '03 last spring.
X2 on the uselessness of all generic manuals - our 2010 Four Winds Freedom Elite 31r has a manual that applies to all TT's, Class A's as well as C's.
Haven't these manufacturers ever taken to the road with one of their units?
Jim