Yes, it doesn't move but the sediments are heavier than the fluid they are suspended in so they remain at the bottom of the tank as long as there is a healthy amount of fuel in it. However, as the fuel/fluid goes down, then the system will start sucking dirt that were originally associated with the fuel at the bottom of the tank.
This is the reason I stall the Benz when I drive it below one fourth. After cleaning the filter and refuelling, I'm OK again.
