Infiltration of rainwater, which method?

So for the pit, a volume of 3.3m³ was calculated.

Doesn't matter. Go to Graf's homepage for example, download the worksheet, fill it out and send it to Graf. Then you will know what you need and what a Graf soakaway would cost.

The one from OBI seems to be from Graf. Here at least for 10 euros more the same and this time it says Graf on it

So, I just had Graf send me an offer directly, delivered by the specialist dealer for €293.78, while at OBI it cost me €279.90, so €13 less. Although Garantia is listed as the brand at OBI, Garantia was actually founded by Graf. The product is exactly the same, also on the Graf homepage; when I go to my product and open the installation instructions, it mentions Garantia.

So this point is already clarified. Just now I was also offered: Universal Filter 3 external ... the whole thing then for a total of €661.81 including VAT and delivery. Compared to €3300 from the earthworks contractor.

I will also have Intewa make me an offer.

I need a total of a 1200L soakaway. It is a soak tunnel of 300L, so 4 pieces in total with an overall length of over 4.64m.

.... regarding your statement that soak boxes can be built deep and igloos only across the surface, isn't that actually not quite correct?

So this soak tunnel is built across the surface and a soak igloo

I'll join in. We're currently facing the same issue. We need to manage about 225 sqm of house roof area and 40 sqm of garage roof area. Graf recommended their EcoBoxes to us. They are supposedly cheaper than the tunnels.
So we need to create an infiltration area of 9.6 m x 1.6 m with a depth of 0.66 m. That puts us over 3k with the Graf EcoBoxes. That's absolutely not doable. I can get it cheaper with any basin.

A question for the experts: Can I also install 2 infiltration systems? Since we have the big bungalow, otherwise we would have to pipe all the way around the house. I would save a lot of muscle power if I basically install a system at every corner.

I need a 1200L soakaway in total

I find that a bit low. In our development plan, 3 cubic meters are already required. The demand is just under 4. What do you want to dispose of in the 1.2 cubic meters?

Regarding your statement that soakaway boxes can be built deep and igloos only horizontally, isn't that actually not correct?

I don't understand your question. Igloos can only be installed horizontally, how else should that work? With soakaway boxes, you can go completely deep if necessary.

So we have to create a soakaway area of 9.6m x 1.6m with a depth of 0.66m.

Quick veto: the hole must be at least 91 cm deep. The soakaway boxes themselves are 66 cm and must be covered with at least 25 cm.

I can do it cheaper with any basin.

Sort of. A basin takes up space on the property and costs gravel. Both are not free either. Of course, the soakaway costs a bit more to purchase, but it’s underground and therefore doesn’t interfere.

Can I also install 2 soakaway systems?

Yes, you can. However, I would rather make one soakaway for the house and one for the garage, driveway, and path to the house.

Just a question for the experts: Can I also install 2 soakaway systems?

I have a total of 5... was easier and cheaper than 1-2 large ones...