How do people keep the clear water pipes under your van clean?Our van is 6 months old and lives in a shed in the dark mostly and the water pipes are looking like they are growing things in them.
Chlorine or Hydrogen Peroxide solution in the tank turn on all of the taps for a minute.
Turn it off and leave it for a day or two then drain and flush really well.
It will do the same with whatever pipe you have, clear just means you can see it..........your house pipes are similar when you cut them open.
But a flush as @NoWorries said will help........................empty tanks when storing won't help either.........best not to look.