I would use ... like beating (or flogging) a dead horse
It even has its own wikipedia entry
I would not use Jim's suggestion beating my head against the wall with the word like - so
I am banging my head against the wall trying to convince him
Trying to convince him is like flogging a dead horse.
are two ways of expressing your problem
If the original is Water naar de zee dragen then it is a sisyphean taskSisyphean task