Install overflow siphon cistern

Hello, I am almost finished with the installation of our cistern. Now the overflow will be connected to the sewer. A siphon from Graf is attached to the overflow. An installation manual that deserves the name hardly exists. Actually, I am only interested in one thing: How can the siphon be secured against being pulled out of the KG pipe, or is that necessary? In normal operation, I don't see a problem, but what if someone has to enter the cistern? With the inlet and outlet protruding into the cistern, the space in the shaft is quite tight and the risk of twisting and pulling out the siphon is quite high. I have considered fixing the siphon and KG pipe together with sheet metal screws. Does this make sense?