You surely know that an underground tank partly filled with a large amount of gasoline is extremely dangerous to tamper with. While the ideas presented here regarding cooling via carbon dioxide or nitrogen are apt to be less unsafe than using sodium hydroxide to dissolve the aluminum, no innovative solution should be attempted without the approval of a licensed professional engineer. The risks can be properly assessed by, e.g., a firm that does gas station underground tank decommissioning.These are 10 to 20k tanks at a regular gas station. New EPA mandates that we check the overfill protection on the tanks. The tanks are buried 3 to 4 feet in the ground thus the steel riser. The drop tube is an industry standard part that has been used for 50 years or more. It is basically an aluminum sleeve that runs from grade to the bottom of the tank to prevent static build up, splashing and in some cases vapors from escaping. Those have to be removed to introduce a new product that has a flapper valve cut in which has a float that raises with the level of fuel and when the tank reaches 90% full the flow from the transport is stopped thus creating an overfill safety device. When the steel riser was new and the aluminum sleeve was new it all slid together very easily but over the years scale, dirt and of course our issue of dissimilar metals bonding has occurred. And yes the new tubes are exactly the same tubes they just have an overfill device cut in at about 10inches below tank top.