For Canon Maintenance Cartridge MC-04 The MC-04 Maintenance Cartridge is a necessary component of the imagePROGRAF W8400 professional large format printer.

It serves as the receptacle for waste ink during cleaning and normal startup subroutines, and is required for operation.
Periodic exchange of the assures the highest quality printing results with your imagePROGRAF W8400 printer.
Your printer's software will indicate the status of your MC-04, and for best results it should be exchanged at ~80% capacity. Product Instruction