I work for BBTS/Waterville. You need to email them and ask. You cannot just show up and sesh, it is not open everyday, you must ask them first. I'm just a coach and I do not deal with any of the planning, so send them an email, it is on the site listed above.
Its a great time tho, so much fun, and now there is a double tramp deck at the bottom of the jump, new two weeks ago. Its fun, hit them up.