when you buy syringes with needles "as one", vs. buying syringes separately and needles separately, can you take the needle off to inject and twist on the needle usedfor withdrawing, and then putting the injecting needle back on?
in other words, when you buy syringes with needles do they come as one piece or do you still have to actually attach the needle to the syringe. i am asking this because i am planning on using different needles for withdrawing and injecting and i am new to this. responses and help appreciated!