OK, first up, the last thing you want to do is not pay your levies as that removes your right to vote and table motions, among other things.
Secondly, this is not about your neighbour who has the right to shower whenever they like. It's about inadequate sound insulation in the pipes of your building (the kind of thing that makes “luxury” affordable). This is a defect that your Owners Corporation needs to attend to and they have a legal obligation to do so.
If they refuse, call 13 32 20 and tell Fair Trading that you want to take action against your Owners Corporation to remedy a building defect.
Finally, the Owners Corporation is every owner in your building, whether they want to be part of it or not. This includes you.
The Executive Committee is elected each year at the AGM of the OC to make decisions on its behalf.
The strata manager is employed by the Owners Corporation to run the building's finances and by-laws. They are usually answerable to the executive committee on a week to week basis but, ultimately, they are employed by the OC.
Owners Corporation decisions always take precedence over EC decisions.
Hope this helps
JimmyT