All parts found at Home depot. Just find the right reducing couplings to get the 3/4in neck down to the threaded lamp tube size 1/8in. Drill hole in side of tank (empty duh) and route wire.
http://www.scubaboard.com/gallery/showphoto.php?photo=19825
http://www.scubaboard.com/gallery/showphoto.php?photo=19825