When I use a neti pot – one side drains out of the other nostril satisfactorily – but the other seems to be completely blocked. I have allergic rhinit

You should never rinse if your nasal passage is completely blocked because this can put pressure on your eardrums. If this is the case (you will know it if you close one nostril and try to breathe through the other) you can use an over the counter nasal decongestant to ease the congestion in the nasal package before performing the rinse. Sinus rinsing should help your allergic rhinitis and could even reduce your need for medication.