Part of the problem is that by the time you have pain, it is already probably too late to do much about it. The pressure differential between the sinus and the outside world just gets too big to overcome. The trick is to clear your ears frequently and before it gets painful. If the pain is present then the best way to manage it is to go back up to altitude and descend more slowly after a decongestant
Otrivine is xylometazoline. Boots do the same stuff but without the trade name and is much cheaper. Would be very wary about using it for more than a few days on the trot as the rebound congestion can be a real problem
There is no one 'cure' but most of the methods mentioned will work to some extent. Keeping the joining passages clear is achieved by reducing swollen tissues with vasoconstrictors (like otrivine) for short term relief and sometimes with steroids for long term management
Keeping the contents of the sinuses (essentially mucus (snot)) thin and watery stops the blockage from getting too bad. This is where the steam inhalations, saline washes and so on come into play. It is worth remembering that maintaining adequate hydration (just by drinking enough) can do wonders for this
Hope that helps
Bob