Irrigate. I assume you mean treating this yourself. Sinus health is all about drainage; if they don't drain, problems persist. You can use a nasal decongestant spray twice a day for 3-5 days; before and about 30 minutes after using it, rinse your nose with saline such as nasamist, entsol, or simply saline. If the sinus pressure increases, or the colored secretions last more than a week, see your doctor.
Many ways. Treatments for sinus infections range from nasal saline irrigation to surgery. You need to find the cause in order to get the right treatment. Not all sinusitis is the same. Causes include: allergies, irritants, infection, structural problems (deviation, etc) and none of the above. See your primary doctor to get started.