What's the best way to treat a runny nose ?

Depends on the age. : If it's an infant, just suctioning the nose with Normal Saline but in older kids 6 yrs and above you can use otc decongestant/antihistamine combo.

Treat the cause: A runny nose may be due to any number of reasons. 1) a viral "cold" in which case you may have to allow "cold" to run its course but you can treat runny nose with drops like nasonex (mometasone). 2) if due to seasonal allergies, treatment with daily Claritin may alleviate allergies and prevent development of runny nose. If concerns for sinusitis, see md.

Ipratropium: Ipratropium nasal spray blocks the mechanism in the nose that produces thin, watery secretions. These can be produced during viral infections, or after exposure to cold air or hot/spicy foods. It can be used on a regular basis, up to 3-4 times a day, or just as needed - many people just use it before going out to eat, so they don't have to wipe their nose in front of people. See your md for a rx.