The first cleaning step is the filtration with the mechanical filter, which retains particles in the water because of its mesh size.
The pre-treated water enters the rainwater tank.
Small particles flow through the filter, heavier particles fall down to the bottom, lighter particles (flower pollen) rise to the surface and float there.
Prevents disturbance of settled sedimentation layer and supplies the lower part of the rainwater tank with oxygen.
This is done with the calmed inlet.
The above floating particles (flower pollen) leave the rainwater tank with the next overflow because your overflow siphon sucks up your water surface. This process is named skimmer effect.
The siphon at the same time forms an odor trap and a rodent barrier.
The cleanest water in the rainwater tank is 15 cm above the sediment layer and 10 cm below the water surface and is removed from there with a floating pump intake.
This is done either with a submersible pump installed inside your rainwater tank or a suction and pressure pump inside the house.