When I open a certain outside tap, and the tap stays open, if you use any other tap in the house - hot or cold water tap - this outside tap seems to "knock". Sounds like the pipe hitting something (typical water hammer scenario I thought). I've replaced all the washers on all the taps in my house, no change. I somehow got this nagging feeling that it all may be due to a sticky valve in the hot water cylinder?
Any-one got better ideas?