Refill Ink cartridge on Dell 720 printer

First you buy a refill kit such as Universal or I-Print brand for approx $10.00. It will refill an empty ink cart 4 times, $2.50 per fill. The full instructions for refilling are in a booklet in the kit. With the 720 carts; For the black ink cart, you fill through hole in top of cart. For color ink cart you have to pry or cut off the top of the ink cart to refill.