PVC inside walls sludge build up?

[monza]

I was switching around some plumbing and noticed quite a scummy sludge in the tubing. Is this of any concern? Should it be regular matinance to clean it?
It would be a real pain on my system traveling from the main to the basement. I have noticed it blow the random amount of sludge in to the tank, the fish seem to like to eat it.

Dave