A Continuous Ink System (CIS) also known as Continuous Flow System (CFS), Digital Image Prints System (DIPS) and bulk feed ink system, is a cost-effective replacement for ink-jet printer cartridges. In contrast to conventional cartridges, a CIS/CFS uses very large (about 100ml/color) ink tanks, which are connected with tubes to the printhead nozzles. The tanks can be conveniently refilled from an ink bottle - there is no need for syringes. The easiest way to get started with Continuous Flow is to purchase a prefilled unit. This means that the ink is already in the cartridges and all you have to do is install the cartridges and start printing. 123 Refills offers prefilled systems for most popular HP, Epson and Canon inkjet printers.

Most continuous ink systems are manufactured around cartridges without printheads. Since the cartridges are connected permanently to the continuous ink system, they should be able to withstand the test of time and durability to last through multiple cartridge print cycles. Cartridges with printheads (typically most HP's for example), will wear and tear faster than cartridges without printheads (such as most Epson and Canon for example), and for this reason most continuous ink systems are manufactured around cartridges without printheads. If a continuous ink system is released on the market for cartridges with printheads, it is adviseable to replace the cartridges every 2-3 life cycles.