Re: M25 what is this and where does the hose go?
The second photo shows the correct manufactured installation. The first one is not correct, and would pull a vacuum on the crankcase and draw oil up through the filter and into the intake in a way that it was not designed to do. Remember, this is a diesel engine, and the intake setup is very different.
It is good to learn from your mistakes, but much better to learn from the mistakes of others...