I got near the end I think, but now I'm stuck. How do I neutralize the tanks?
I made a screenshot since that's probably easier than trying to explain where I am.

You're screenshot isn't very clear.

It looks like the final level where you can peek outside and see a tank.
You have to do some running there.

I had to use a walkthrough a few times during the game in order to move on:
http://uk.faqs.ign.com/articles/453/453739p1.html

I neutralized the tanks but now I can't get past some kind of gas leak. Did I miss something from before? I can't find the place where I need to turn off the gas pipes.