Onions. Onions can be an effective remedy for postnasal drip. The compound quercetin found in onions has powerful antihistamine and anti-inflammatory properties. Onions can act by helping to break up and clear mucus from the body. To relieve symptoms of postnasal drip, try adding raw chopped onion to broth. The warmth of the broth along with the onion can help to clear congestion from your sinuses.