I am having print dramas. The tube delivering ink from one of the black cartridges is clogged. Installing a new tube is complicated by for the person who services our printer by a lack of parts. 7 days is the quoted delay. They are reluctant to try to clean the tube. If I tried a bit of DIY is there any advice concerning obvious dos and dont's – will the system need to be bled of any air for example and if so how. Theo Stegers