You'll need a 16mm socket on an extension. The torque setting (official) is 21lbs/ft. on a cold head.(I've read a 'rule of thumb' that says a quarter of a turn after feeling that you're gripping the crush washer will not be overdoing it but can't say from experience as I'm new to the
MCS.) I plan to do this and check tightness whenever I'm under the bonnet as, apparently, there have been reported cases of plugs very occasionally working loose. Hope this helps.