Oh Level 9, how well I know ye. I know ye nearly as well as the back of my hand, prehaps better. Might I ask what your concern is?
Which "Bottom" are you on?
Are you in the tank, because if you are in the tank you must shut both doors before you can open the other one.
If you are not yet in the tank, to gain access to the tank you must change the level of the alternate tank, by using the switches, the one where you enter the complex works nicely, if I remember, it's been a few years.