Re: 4 holes in bottom of stem?
If there are four holes at the base of the stem that goes in the water is located. It is called a common chamber. Meaning the heart of the hookah is hollow and the hose port and purge valve use the same holes. If they were seperated and the heart was solid it would be called a traditional chamber.
IMO and experience common chambers are ok, but dont purge well at all and can rust up easily and quickly. If you have the chance to go with a traditional chamber hookah. I highly recomend doing so.
(*Disclaimer* These are my opinions and mine alone. It does not reflect the opinions of others and is based on my personal smoking enjoyment and experience)