[@Dervish]

Your guess is as good as mine. Luckily I don't work that job, but whenever I've had to be near an open septic (one time I ended up helping them out with a few things, mainly out of curiosity) I had to break out the [url=http://www.legionsafety.com/images/T/mm6700din_1.jpg]3M mask[/url] >.>

I'll stick with blowtorches and metal grinders. Roughly the same chance of a rogue spark setting off an explosion but a lot less smelly.