How do I find the password in that gangster hideout after riding the garbage can?

Welcome Mike_B
I moved this to the right forum.

You probably haven't gone everywhere that you can go... you'll find somebody who knows the password and will tell you, then you can go back and proceed at the password point

What Prime said.

If you REALLY cant find what you need to do, read further down
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When you get into the ventilation system which is located in the corridor before you enter the upper level of the compactor room, you can see through bars there is a greedo-type enemy there and an exploding crate next to him. Shoot the crate. Voila.

To find the password you have to go around until you find your way into the holding cell area, there you will find lando and he will tell you the password, then you can get in