I'm with Tracey on this one...let it run! Yes, I have experienced this sort of drainage before...messy and uncomfortable, but it is a good sign (of course, assuming that you haven't caught a bug)!
You might want to try using regular nasal washes...this is a yogic practice called neti which uses a very diluted salt water solution that you pour through one nostril and it comes out the other. I know...it sounds a little scary, but it's easy, painless and it works great at clearing out mucous, toxins, pollens etc. Run a google search for neti...you can pick up the pots at most health food stores.