Tap water or sterilized water doesn't matter since your ear
canal is not sterile.
Either will work. Make sure the water is not very cold or very hot. This could cause a reaction with your balance centers and make you dizzy and vomit (not permanently harmful, just unpleasant). Two things to note before you flush: first, make sure your ear drum is intact (a doctor can tell you this by examining you). If there is a hole in your drum, flushing your ear with water can cause water and germs to go through the hole into the middle ear and cause infection. Second, sometimes the water can just push the wax further in towards the ear drum instead of out of the canal. If you have a large wax impaction, you may be better served by having an ear doctor (otolaryngologist) use a microscope to pull it out manually.
Legal disclaimer: I am providing this general and basic information as a public service and my response to this question does not constitute a doctor-patient relationship. For any additional information, advice, or specific concerns, please speak with your own physician. The information provided is current as of the date of the answer entry.