What should be the connection betwe

The connection type of the hose to the ball valve can be either screw joint or flange, which may be based on the hose size, process condition, material availability, etc.
No way to know what's the better setup as you didn't specify what are the application conditions or any requirements.

@mk3223

The application is sewage water removal. The size of the line is 25 mm

Per the hose size of 25mm, the screw connection can be used if it is not a hazard or risk operation. May hang the hose loose at bottom of the pit, if there is no danger to the personnel or equipment.

That size and application: neither, use hose clamp for easy removal and cleaning. Other connection depending on environment use/use. What about having the hose outlet end secured and steered by putting the hose end into a (fairly) larger dimension firm pipe fastened to the (side wall? top cover?) of the pit.

@gerhardl

Yes, I thought of doing that set in the pit. But that is not the connection used in the old plant.

@gerhardl

Is this the connection you mean between the valve and the hose

Yes, but all would be depending on surrounding, technical and practical circumstances. No absolute answer.

Well it must be pretty "clean" sewage if your line is only 25mm diam... It's not clear if this is delivering sewage or removing it from the pit.

If your pipe connection can handle the weight of your pipe full of water then hanging it loose is Ok, but might look bad depending if there is any movement.

If you are pumping in then I would fix it to stop the jet of water from moving the hose around, but depends on your velocities.

Connection? - Up to you - what ever works. Usually imposed by whatever the hose connection is that it comes with. A machanical joint is a lot easier to undo and replace, but not "required" if a clamp is good enough.

A picture would help....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.