I clean carpet for a school district and we use a Tannin remover for this. If applied correctly and rinsed right it works wonders, another choice is a citrus based product. It is available at Janitorial stores and maybe places like Home Depot or the like. Blotting will work fine if you are patient, but extraction is much better. All you need for that is a wet vac and you can apply the water and chems by hand.