Very interesting. The idea of him ending up in a tank brings me back to Elisa Lam's case. I wonder if it would be possible to find more info about the tanks to see if falling in one is even possible. I assume there are a lot of safety precautions with the design of the tank. Maybe with the manufacturer info it could be seen if there is a way to accidentally end up in the tank. Based on the timeline of his disappearance, I do not think he made it far (with the no foul play theory).
I'm sure on newer tanks there are all sorts of safeguards, but the lions share of tanks I saw in the area looked to be extremely old. The Salt Flat oil field was discovered in 1928 so a lot of the structures are from a time when safety precautions didn't exist.