Back in the 50/60/70’s my Dad was a licensed hazardous removal/ explosives guy. He tangled with a few of those old Pre war underground tanks and they were, indeed, some tough stuff. Sometimes gas stations got moved when roads got widened. Don’t know that he ever found a leaky one but part of the removal was that they had to be de-milled so they couldn’t be used again and cleaned enough to be scrapped. His method was to dig ‘em up, hoist them out, and haul them outside town. Put enough dynamite in to make them rupture, then torch them into small enough pieces to scrap. Dad made up a lot of his own rules. Sometimes a County guy would come around and make a “suggestion.”
I always guessed there was a good reason for those tank filler guys to use a wooden dipstick——so’s they didn’t dink the bottom of the tank?
Back in my gas pump jockey days, we used to stick the tanks daily with a wood stick when we read out the pumps. The amount pumped need to roughly match what was used up from the tank that day.
Besides checking the depth of the fuel, we also checked for water - we smeared a special compound on the lower 4 or 5 inches of the stick. It would change color if it found any water. There was a certain amount that was acceptable, but I can’t remember what it was. Condensation inside the tank, settling to the bottom because gas is slightly less dense than water. Didn’t get to the customer’s cars because the pickup floated near the surface of the fuel, not at the bottom of the tank.
If the water content was too high, we’d run it down, then pump out the tank and refill (had to have someone come and do that - we gas pump jockeys didn’t have that skill nor the equipment).
Sticking the tank also measured the depth of the fuel vs what it should be - that is, we’d compare the amount in the tank versus what was supposed to be in the tank. We’d also stick them immediately before and after a delivery to make sure we weren’t getting shorted. We had charts of inches vs gallons, taking into account the shape of the tank, of course.