Drill an additional inlet in the rainwater inlet box?

Hello everyone,

I am currently thinking about the best way to drain the roof area of the soon-to-be-built carport.
At a distance of 4.5m from a possible post for the drainage, we have such a rainwater collection box installed for the downpipe to drain the house roof:
[IMG width="185px"]https://m.media-amazon.com/images/I/61Cr0iIPwyL._AC_SX679_.jpg[/IMG][IMG width="213px"]https://m.media-amazon.com/images/I/51veIrweQpS._AC_SX679_.jpg[/IMG]

Both the rainwater collection box and the post of the carport are located in the eaves edge.
My idea was to lead the drainage from the carport post to the already existing collection box. However, since the pipe should preferably not be visible, I would have to lay it under the gravel in the eaves edge.
A 2% slope over a distance of about 4.5m means a height difference of 10cm, so I would have to make an additional lateral cutout at the lower end of the box.

Do you see any problem with that? Possibly with sealing the additional cutout? Maybe someone has already tried this themselves? I couldn't find any ready-made boxes with an additional lateral inlet.

Installing a T-piece below the rainwater inlet box is not an option?

Is installing a T-piece below the rainwater soakaway box not an option?

I thought I could use the sieve of the rainwater soakaway box at the same time. There aren’t any tall trees yet in the new development area, but I would be afraid that it might get clogged after a few years otherwise. The water goes into such buried soakaway boxes and not into the sewer system.

You can just install a sieve/separator at the carport, it doesn't cost a fortune. Only then do you have it clean without a makeshift solution

The drainage is hidden in the post. In other words, there is a DN75 outlet relatively low on the post. From there, I can continue.
I have only seen such cut-offs used for installation in the downpipe so far. Are there other possibilities? What should I be searching for?
Of course, one could use a second rainwater sump, but then I would already be very deep at the eaves edge at the beginning and would have to dig up quite a lot again.

If it's just about leaves, then simply install such filter baskets on the carport in front of the downpipe. They are simply slipped on and that's it. They come in all varieties.