Right of way for wastewater channel from neighbor

Great attitude! Do you have to get something out of everything? If he has no disadvantages, you could just be nice and pull together as neighbors on a "sewer" line.

With such an attitude, you become extremely popular in the neighborhood... I almost had a similar case, a neighbor had to run his power cable a few meters over our land (in a place where it didn't bother anyone). Everything was formalized, he bore the costs and there was a certain "hand money" as compensation.

However, it must also be noted that a land registry-secured right of way for utilities reduces the property value. Whether it is an electrical cable, a water pipe, or a possible right of way. The property may then possibly no longer be built on as before, repairs may be necessary, which then requires major civil engineering work. Likewise, tree roots can damage the sewage pipe, and then the neighbor is left with a hefty bill at the house. If you then want to sell, such a right of way can quickly have a negative financial impact. Of course, the neighbor can try to lay their line anyway by invoking a right of necessity.

Not only in the land register, but especially in the [Baulastverzeichnis]. This also concerns public law. The strip remains unbuildable!
All the other issues with maintenance and civil engineering are secondary; these must be borne by the neighbor or the owner of the dominant property. But the restriction of being able to freely use less and less of one’s own land weighs heavier. I have something like that (although I consciously accepted it when buying) and have somewhat masked the circumstance by also using (– will use) the driveway. But de facto, I have 60m² less property because of it.

However, it must also be noted that a registered easement in the land register reduces the value of the property. Whether it is a power cable, a water pipe, or a possible right of way.

A simple easement or similar is value-neutral. Any appraiser will tell you that.

The property may then possibly no longer be built on as much,

Only if you place the rights within the building area. But they belong in setback areas or outside the building area. Then you can use your property completely freely.

repairs may be necessary, which then of course requires major civil engineering work. Likewise, tree roots can damage the sewer line and then the neighbor is faced with a hefty bill at the house.

These are exclusively problems for the one who holds the easement. Even YOUR roots are (almost) always their problem. There are numerous court rulings on this up to the Federal Court of Justice (BGH). The neighbor has a big bill including civil engineers and landscape gardeners for work on your property. But he is allowed and must pay for it himself.

If you then want to sell, such an easement can quickly have a negative financial impact.

No. With every normal easement or similar, and many properties are encumbered by such, the right has no effect on the purchase price.

Of course, the neighbor can try to lay their pipe using a notrecht (emergency right).

They can try, yes, but not successfully. There is no reason for it. After all, he has a septic tank.

Not only in the land register, but especially in the Baulastverzeichnis.

No, not normally.
By the way, not every federal state has such an outrageous Baulastverzeichnis.

Thank you very much in advance. I’ll get in touch when the kids are in bed. By the way, we are building in Saxony, in case that should be relevant.

Don't do it. Don't do it.

Even though I am in favor of a good coexistence and do not intentionally put obstacles in anyone's way.

My uncle has a property where the neighbor's freshwater supply runs across it. Diagonally over the property, because decades ago that was the simplest and most direct route and the property was completely undeveloped.

BUT now, after 20 years, he wants to build himself. The pipe must now be laid along the public road. Digging up and re-asphalting costs... and of course he has to pay for it.

In my case, the sewer, water, and electricity of my sister next door run across my property. Because of the pipes, caution is required when planting trees there. A tree would have been really nice at that spot... and according to the notary, the right of way constitutes a depreciation of value. In our case, this is currently irrelevant, but also for future generations: let boundaries be boundaries.