"Take the tube and submerge it in a 10% bleach solution, ensure the tube is full of the solution. Leave it for 30 mins. Then give it a good blast of tap water, and finally soak it in clean water for 30 min to get rid of any bleach, and it will look good as new
I do it with my all pipes when they start to get mucky, Co2 diffusers and with my glass poppy intake on my nano tank. Works a treat, and will not harm your fish, given that you have rinsed and soaked any residue away with clean water."
DevotedToDiscus gave me this advice. Yeah the pipes do get filthy. Just another part of the maintance schedule.