There's nothing like the direct approach, right? Well, short of a pipe snake, using a nasal irrigator or bulb syringe to flush built-up mucus from your nostrils and nasal cavities is about as direct as it gets. The key to this method is to keep both the water and the device sterile to avoid bacteria. You can buy irrigation kits at the store.
Alternatively, try one of those teapot-looking devices called neti pots. Just lean over a sink, cock your head at a rakish 45-degree angle and pour away. Adventure awaits, as does an anatomy lesson/party trick, as the saltwater runs from one nostril to the other via your nasal cavity. It might also run into your throat, so prepare yourself for that possibility [source: Doheny]. Ta-da! Who says you don't know any magic tricks?
Sinus Congestion Tips
Here is some information to help you with sinus congestion.