Those worm castings are junk for tea in my opinion. When you raise worms, you get fresh bacteria, fungi, and the compost/castings that come with them. From the store, most of the best bacteria have died off and there's hardly any fungi, if there's any at all.
You can use the store bought ones to make a tea to feed with, but it won't be as beneficial with all the bacteria. Even homemade compost without worms has more bacteria.
Fill a pantyhose up about halfway, tie it off to the bucket, fill it with water and a cup of sugar, stir it up, and bubble for 24hrs. Then dilute it 10:1 and feed.