ᐅ Clogging Beneath the Foundation Slab – A Mystery

Hello everyone, we have been living in our house for 9 months now. We are experiencing the third blockage below the slab foundation. The pipe runs under the foundation across the yard to the drain. From the drain to the house, there are no signs of damage or blockage.

There is gurgling throughout the house, and all drains are very slow or not draining at all (including upstairs), except for the kitchen. We notice the blockage because the toilet siphon upstairs loses water. So far, we have been able to clear most of the water buildup using home remedies. However, it now seems that there is a serious problem in the main line.

Now the puzzle:

When we run water in the kitchen, it reaches the drain without any issues. Everything else does not reach the drain. When we insert a camera into the drain in the utility room (the camera from a friend is too large for the other pipes), the camera is submerged in water after 2 meters. The kitchen is located beyond the utility room when viewed from the drain connection. How can this be explained? What could be the cause of the problem?

Image:
K Kitchen
H Utility room
E Ventilation pipe, which is also connected to the bathtub

The guest bathroom connects from the left side of the stack.

Is there a wastewater plan for the building permit / planning permission?

This won't help you much, but I always warn against routing under the slab.

How many of the lines are vented through the roof? Are you already familiar with the information that appears, for example, when searching for "standard-compliant drainage IKZ"?

Where is the upper floor bathroom connected that is causing the trap to drain?

That should be where the grounding rises. The shower on the upper floor, as well as the washbasin, I believe connect to the stack at the vent pipe. Only the toilet then goes down there.

There is only one vent pipe.

I just read the requirements according to the standard.

Show this to a qualified plumber. I think the ventilation is insufficient, possibly in combination with inadequate slope beneath the floor slab.