In this How Too by Wild_Willy he says to use a Jayair Universal Heater Tap # HA4008. Well this has been superceded and the new replacement is $44 and I'm told has plastic parts similar to the current Holden which break easy.
Currently Repro has the HA4008 on clearance for $11. There were only 4 left in SE Qld - 2 at Beasudesert and 2 at Beenleigh ( now 1
) In other states check with your local store and if they don't have it ask which store does.