Brilliant! You tap into the tree at exactly this time of year!
Or in april, depends on how warm the month of march has been where you are. It is very simple; the same procedure as when tapping maple syrup. The birch syrup is clear, and tastes wonderful. Very sweet, and therefore dilutable. It is best used in spring. A friend of mine taps it every spring for other purposes than cleanse, she just makes a pitcher of water and syrup and drinks it all the time. ( I think that the Weleda readymade one also contains blueberry)
If only I had a birch tree......
good luck! a-m