If by cleaning you mean old fuel and general crud google fuel tank cleaning. There are a number of products on the market. Another option if there is a radiator shop that will do it is to take it to a radiator shop & have them put it in their chemical tank. No shop around here will do that. If by cleaning you mean a lot of rust there are kits for derusting and coating the inside of the tank. I use Kreem on a motorcycle tank years ago with success. I restored the tank in my 38 using muriatic acid to remove the rust, brazed the larger holes then coated the inside with Redkote. Four years so far with no issues.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.