Franke Ascona 1.5 sink installation

I will soon be fitting my Ascona sink (model 651).
No instructions came with it concerning installing the waste system. No instructions available on the Franke web site.
Franke central services tell me to put metal to metal on the inside of the sink and the rubber washer between the metal and plastic waste connector before simply screwing them together.
Does this sound right? I have seen videos with people using a seating compound (plumbers putty) between the sink and the waste connector (inside the sink).
If I am to place metal to metal, how tight must I screw the parts together to avoid leakage between the mating parts and avoid stripping the thread on the plastic part of the waste connector.
Your experienced advice will be much appreciated.
Tks.