gingernut, we think alike but if needs must.
Now a regular swim in a nice clean swimming pool then hang your head over the side and let the sinuses drain naturally.
Seriously, I used to do reasonably deep snorkel dives for an hour or so. Later, in the bar say, I may bend over and there would be a great gush of water out of my nose 'yuk', but at least I knew the sinuses were running free.