The best tap for me is actually a sharpened stick about 2 match widths thick and one and a half lengths long sharpened to a point at either end and when you make the cut the least intrusive and damaging way is to place your knife at a 45 degree angle with the blade facing up and bang the handle with your palm, you'll be aiming for about 2 inch penetration, as soon as you do this you'll get sap running down your knife, you need to then place the tap you have already made up into the slit you've made and then adjust it until your drips are coming right off the point, lash a vessel to or under the tree to catch the drops, I find a 2 litre bottle well tied under the rim of neck does the job, then overnight it is possible to gather anywhere between 1 and 2 litres, during the first 2 weeks of march the sap will really be flowing so this will be your best time to harvest, and boiling down will make a lovely syrup or drank on it's own it's a really refreshing slightly sweet drink, natures good to us if you know where to look and how to treat it, plugging the wound should be done with a clean shaved stick suitable to the size of the cut, don't worry if there is still a slight flow as it will heal over naturally the trick is to stop it from gushing as an open wound can lead to infection in the tree.
would be nice to hear how a beer goes with it :)
