No easement for sewage available

Hello everyone,
I hope I have come to the right section here with my topic.
We are interested in an existing single-family house and would like to buy it.

But we have discovered a problem with the course of the wastewater drainage.
I have sketched this out - "our" property would be number 1. Properties no. 2 and 4 each have a right of way for wastewater registered in "our" land register. We know nothing about no. 5. We also do not know how many houses beyond that are also connected via this pipe.
The big problem now is that property no. 3 (over which we must drain the wastewater) has no pipeline rights registered in its land register. Property no. 3 has a direct public wastewater connection at the street. The owner of property no. 3 does not want this pipeline right to be registered in the land register.

As we understand it, there is a risk that no. 3 could eventually remove the wastewater pipe since no pipeline right is officially recorded in the land register.
That means we would receive wastewater from all neighbors (who knows how many households dispose of their wastewater via it) up to our property? Does anyone of you have experience with this or can help us whether that is actually the case? Theoretically, one could also sue for an emergency right of way. However, whether this would be successful is uncertain.
I will call the AZV tomorrow and get some information.

Everything already in stock or is new construction included?

No. 4 is a new building, constructed two years ago. The rest is all old stock.

What did the AZV say?

I have not come across such a constellation before. In the course of the new construction, we relied on the handover shaft of my parents (neighboring property) and received advice from the notary to register an easement for this. However, we initially refrained from doing so because it would hardly be a problem for us to retrofit it quickly in the worst case.

But in your case, does this mean that property owner #3 has so far tolerated the drainage through his property? I can only imagine that this was once a friendly community project and now, as properties and houses change owners one by one, #3 no longer sees any reason to tolerate this forever. So I would definitely try to clarify this finally before you buy there. In the worst case, you might have to lay dozens of meters of new sewer pipes, create a new handover shaft, and so on.

An excerpt from a site plan would be helpful to make the whole thing clearer. Where does the public sewer run? I can’t imagine that there is a law allowing the neighbor to channel his sewage through someone else’s property?! But maybe I’m mistaken there too.

I'll throw two things into the room:

1. In order to build on a plot of land, it must be developed. Without development = possible connection to the sewage system, construction is not possible. Therefore, during construction, at the latest at No. 4 as a new building, the approval authority should have checked and approved the development.
2. Development charge. The pipeline right does not always have to be registered in the land register. A charge can also exist.
3. Perhaps an easement was notarized a long time ago as part of the construction projects at that time but was accidentally never registered. I have also come across such cases where a servient property was simply forgotten. However, tracing this will be difficult.