Neilmed is a great suggestion, however...
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http://en.wikipedia.org/wiki/Nasal_irrigation
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A pulsating irrigator works much better for me, and probably would for most people. A good way to weird people out, really.
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I make my own saline solution. Sometimes I make it slightly hypertonic. Other times I actually put a drop of betadine in there, or even tobramyacin. I haven't had to take antibiotics for a sinus infection in several years... and this is coming from someone who has had four sinus surgeries in the past.
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Your dad will probably have to have the surgery done, but fortunately he's likely to never need it again if he keeps up with the sinus irrigation.