95 Ford F150 losing Fuel

My husband and I recently purchased a used F-150 with about 130k miles in immaculate condition. It has been a great truck up until about a week ago. It has dual gas tanks and it appears the front tank is losing fuel from somewhere. There are NO visible leaks, but he had put $22 in it and by the time he got home after driving to and from work (not very far) he was on empty. This does not seem to be the case in the rear tank. A mechanic friend of ours put it on his computer and no codes came up but he didn't have any other ideas. Any help would be appreciated as gas is tooo expensive to be losing it that quick.