You need to get info on the exact laws in question. If the law only states it is illegal to purchase and own something, you are not breaking the law by servicing the tank because you don't own the tank or its contents.Well if you know it's illegal to keep one smaller than 3 feet and you service a system with one less than 3 feet then yes I would have to agree with your friend. @Katrina71 might have more insight to the legality of the issue...