Water Tanks, page-112

Zero said........
"Never heard of a wet area, fast flowing water will NOT deposit sediment, and it sounds
like everyone is over complicating catching a bit of rain water"

and
"Never had a "wet area' on my tank. Never heard of one 'till here."

and
"Re. wet systems, if there is heavy rain, and a large catchment area, it is impossible
for sediment to 'settle'. The only time sediment will settle, is when the water stops flowing."

Well zero,
now that you have heard of a wet section of pipe let me try and explain how it works.
The water speed through the gutters and associated pipework is considered to be the fast flowing water in the system.
If you look at the photo of the sediment trap supplied, you can see that the U shaped section with the drain attached to it is able to fill up with water to the height of the original down pipe section which runs along the shed to the tank. Ideally this section should be a bit longer to allow more time than I have but the room was limited.
This means that the water flowing through the wet section, because it is now travelling through a 90mm pipe, is travelling a lot slower than the water that is travelling along the gutter. Because the water has slowed down a lot, it gives the sediment time to settle out into the drain section of the trap.
You must be aware that as the water has been travelling along the gutters and pipework , the sediment is already beginning to settle to the bottom. It does this because the water that is closest to the walls of the pipe or gutters travels slower than the water that is in the centre of the pipe. This  characteristic is called that the water travels in a laminar flow.
The sediment slowly accumulates as it goes along and builds up into small patches of sediment on the floor of the pipe.
If you make the wet section out of clear pipe and put some food colouring into the water it is really easy to see this happening.
The other thing you will notice is that, as the small patches of sediment build up on the floor of the pipe, they eventually get too much resistance and they break away and are move along to the next little patch of sediment. This then creates the same scenario and so on and so on. Once the slowed sediment hits the wet section it is no trouble at all to see how the sediment "falls" into the wet drain section.
Opening the drain is no different from you changing over your grey water diverter. By the way, I would never have a grey water line connected to a drinking water line in any way shape or form while ever my ass points to the ground. To me this is a perfect example how problems can occur.
Hope this helps.

Lucky.

"all is not always as it seems"