Don't do it.

They used to tell people to get the tank filled with sand and certify it as abandoned. HOWEVER, and there are multiple cases about this (just look them up), if there is any contaminated land, it doesn't matter that it was certified abandoned if it's still in the ground. YOU ARE ON THE HOOK FOR IT, and you will pay thousands of dollars to fix it.

My partner's former boss had this issue, and they ended up paying nearly 100k to resolve it. It was a fucking nightmare.

When we made offers on houses, we stipulated that the owner had to remove the tank. If they said the tank was removed, we pulled the permits to prove it, hired a company to do a tank search, and had the soil tested for contamination.

Again, don't buy a house that has a sand-filled tank if you're not willing to do the above.