how is it possible the cops didn't look into the tanks??

She is mysteriously missing in a clear and limited area (the hotel building), at one point he says there were 18 cops for like a day looking everywhere on the 15 floors, and that they had checked the roof, seriously no one thought to take a few minutes to go check inside the tanks??

Even after several days when they were absolutely sure and convinced that she had not left the hotel they still didn't think to have a quick look in the tanks??

Weird and hard to believe.