Ugh! I had the worst post nasal drip all of last week, after getting over the flu and a sinus infection - it was as thick as pudding.
The best thing for me was my Neti Pot. It flushed the nasties out and stopped the PND for a few hours at a time, and you can use a Neti Pot up to 4 times a day. As long as you follow the instructions carefully, it should help fairly well. I'm so pushy when it comes to Neti Pot safety - make sure the pot is sterilized by washing thoroughly and microwaving it for 2 minutes before using, and only use distilled water.