Backed-up sewer line in rented apartment - Germany

The sewer line in out apartment has backed up and the landlord is refusing to hire a plumber. Any suggestions on what our recourses are? Under what conditions is a renter responsible for paying for plumbing in someone else's property?

I don't know what your landlord's responsibility is, however, I've always called my own plumber in the places I've rented here in Germany. I called them to unclog drains.

I would assume (read: I am not sure) that it depends on what caused the clogging. If it was your fault, you pay, if not, present the bill to the landlord.

but find out who he would hire if he would do it, coz he can decline to pay it if you use a different company, or so i've been told

The landlord is responsible for the apartment being suitable for use. If the drains are blocked the apartment is not suitable and you are entitled to reduce the rent.
Gut feeling: The landlord calls in a plumber to remove the blockage and at the same time find out who caused it. The landlord then claims the costs from said person.
Confirmed http://www.urteile-mietrecht.net/Abfluss-defekt.html
Advice: All of the tenants get together and remind the landlord of his responsibility. There is strength in numbers. If 20 parties reduce their rent by up to 20% the landlord will be a very unhappy kitty.
Disclaimer: This is a lay opinion, ask a lawyer.

I never expect my landlord to pay to unclog my drain because it my thick hair that is clogging the pipes.

The Landlord is responsible.If he however can prove that certain persons have been abusing the sewer systems then he can ask you to pay a certain amount towards the bill.We had this problem in our last apartment when a silly woman kept throwing her sanitary towels down the toilet.She was a bit loopy loo and only flushed her toilet once a day.If the landlord is refusing to pay then give him a ' Frist ' of 3 days to get it sorted out.If not then you are going to get someone to come in and do it sending the bill on to him.Make it clear that you will pick a company out ofthe yellow pages.The landlord will move his arse then as he will more than likely use someone he knows that is cheaper.

We ended up calling the plumber that the landlord uses. He snaked the drain and found a clog 25 meters out. That is farther away than our house is from the street.

The landlord says we have to pay because no one else uses that plumbing line. There is a washing machine and a toilet connected to it. The toilet is only used on occasion because it is located in the garage. There is no way my husband and I could have caused this problem.

I have never had a landlord try to get me to pay for plumbing problems before. At home that is the landlord's responsibility. But, this is the first place I've rented in Germany. The plumber's advice to us was "clean it real good, and move as soon as you can".

You have the so-called Schadensminderungspflicht, the duty to keep damages low. Get three estimates and pick the lowest one that still provides the full necessary service.

@ Mishell - If the clog is that far out I should think it's a municipal thing. Get in touch with your local waste management.