"When I was in my early twenties working for a building company in Manchester in the late sixties, I had two bottles on my desk, each with a nail inside. One had Fernox inhibitor and one without. The one without had cracked the bottle with rust. Thus today, I buy Fernox F4 leak sealant assured of a company whose pedigree is second to none. For me, it is the go-to leak sealant, also second to none."