Originally there was a LOT more to the backlot tour - if I remember correctly it used to be over an hour long! After the water tank they walked you past windows looking into real (and occasionally active) soundstages and production facilities, among other things, and a short green-screen segment involving riding a giant bee from Honey I Shrunk the Kids. (something that was in direct competition with that other studio's park riding a bicycle with E.T.). Also you got to see props and sets from films - I remember sets from 101 Dalmatians with Glenn Close, and the subway car from Speed were there at one time. And then you got on the trams, through the boneyard, went through Catastrophe Canyon, and down residential street and drove around the square at the end of the city street - city hall was from Back to the Future, and there was a replica of the arch from NYC.
They broke the tour into 2 parts sometime before 1996 - The Backstage Studio Tour (25 minute tram ride) and Inside The Magic Special Effects and Production Tour (40 min. including water tank, giant bee, soundstages, and the Bette Midler short film "The Lottery", concluding with a walk-through of the interior sets from the film.
Of course, now it is much shorter and residential street is demolished. The water tank is still fun, though, especially if you get picked to act!