Jackson wrote:
When you screw in an outside tap into the wall plate, how do you
ensure that the tap is screwed in very tightly to the wall plate so
that it will not move or leak - and the tap is itself vertical?

Tighten it up onto the wall plate beforehand, offer up to the wall, mark the
screw holes with a pencil, drill, plugs then screw it on, then plumb to it.