In the user manual for the Pure, it describes how a positioning strap is looped over the tank valve and tightened. No problem there. What i don't understand, though, is the next line in the manual. "This will help you position the BC onto the tank on your next dive." How does that work, when the strap has to be undone to get the tank off, thereby eliminating any "fit" you might have achieved over the first tank?