What's the best method for relieving sinus pressure?

First, diagnosis: How do you know you have sinus pressure? Is the pressure under the eyes, between the eyes or above the eyes or in the middle of the head? Correct diagnosis comes first and if there is nasal discharge that is yellow, it can be cultured and an appropriate antibiotic given. The gold standard of diagnosis of sinusitis is a cat scan. My emphasis is on getting a diagnosis before treatment.