Draining a sink into rainwater gulley (combined drainage)

[bandejapaisa]

Can anyone inform me of any regulations regarding draining a sink into my rainwater bottle gulley. The gulley grate or sides don't have any closed sockets for me to connect to. Does the pipe need to be below the grate, or can it be above? I'm sure I've read something about this somewhere, but can no longer find the reference.

Previously, the sink pipe was just pointing above the top of the grate and flowing into it. Are there any specific products I can use to make it more tidy?

It's a combined drainage system.

 

[jj4091]

Ours use these https://www.bes.co.uk/black-polypropylene-round-grid-180-mm-dia-polypipe-13404/ with the above ground wastes going through the cutouts by an inch or more