The idea of having a stoptap rather than a lever isolation valve is that the loose jumper acts as a non return valve in the case of backsyphonage. It's the last defence before any polluted water hits the mains. {This is the moment when all trained plumbers remember that seventies training film where the woman leaves the hose running into a bucket with weedkiller in it.}
I have fitted drain off valves on many occasions but I cant remember ever using them.
As a result of the many other occasions I haven't fitted them I have never ever been arrested by the water police.
I have fitted drain off valves on many occasions but I cant remember ever using them.
As a result of the many other occasions I haven't fitted them I have never ever been arrested by the water police.