the idea behind tree tapping is to tap a knife or other sharp piece of metal at an angle under the bark of a tree, wedge some kind of straw or metal sliver into that hole and set a container of some kind to collect the sap that will drip out. you can safely get about 12 oz or so from a tree per day without overly worrying about harming the tree. the sap is only good for about 18-24 hours before it starts to go rank due to the sugar in it. the best trees I’ve used this method on were poplars.
in the game this would probably be classified as some kind of ‘sweet water’ and would have a low level of nutrition around 5 or so and a quench of around 40 and enjoyability of 2 or so.
if you find yourself far from rivers, swamps or buildings with ‘fresh’ toilets, OR if you don’t have a way to purify the water, this method could save your toons life.
you could even boil the sap-water down to get a small amount of sugar for crafting.