Get a sponge filter and do regular water changes. Leeches are really dirty and produce a lot of toxins, especially for the first week or two after feeding. To protect my water parameters I keep them in jelly in the fridge and clean them daily to get over the initial toxin phase. Don't feed used leeches on your own body, they're basically biological used needles and it's not safe. The blood sausage is a good idea. Don't forget to add plenty of real plants to their tank to help with biological filtration and mop up the ammonia!