This is a picture of my rainwater harvesting tank.
Note the downpipe coming in from the right has to cross a vertical soil pipe, this acts a silt trap.
Inside the top of the soil pipe is a piece of plastic drilled with holes that acts as a baffle, behind this is a mesh screen to stop debris entering the tank.
On the top left with the white tape is where I first had the overflow pipe, that was way too high, so it is blanked off, if you look closely, below and to the left that is the new overflow, it goes underground and ends up in a soak away.
I am thinking of altering the downpipe so it enters the vertical soil pipe lower down, this might help in keeping the filter cleaner, as any debris that enters the soil pipe will be underneath the filter and suspended in water, which I hope will sink to the bottom.

Edited to read 1200 size not 1300.
Allen..