Digital BW, The Print

I own an Epson 2100, my first printer. I would like to save the ink 
(and cart) from an cart when the printer says its empty, and use it 
again when the same colour's cart is empty again.
I see several methods/workflows and tutorials to do this, and some 
mention of a sponge in the cart that may complicate the issue. Can 
anyone recommend a method to re-use carts and save ink from one to 
inject into another, that would be appriopriate for the 2100?

Andrew Lee