What codes and regulations are involved in the building and design of a small unleaded gasoline transfer system and storage tank?? (20 - 25 gallons) Where would I find them??
Well, it would probably help if you told us where (what Jurisdiction) the project was located in. Might make a difference if its installed in Philadelphia vs Uzbekistan or Texas.
From a strictly engineering perspective, you might find this useful - and not too expensive.