I think the bottom line is: if you don't have a specific need to
irrigate; don't irrigate. ...Give your body a chance to build up its own
protective system.

That being said. ...When I irrigate, I fill the pik continer about 1/2
full. ...Normally, any infective material is usually flushed out almost
immediately.  ...However... The idea behind the water pik usage is that
the moving liquid creates a low pressure within the sinuses, which
ultimately helps to facilitate the natural drainage process.  ...Also,
as Dr. Grossan has pointed out, the pulsating action helps to restore
the cilia within the nasal cavity.   ...Jon

Each time you irrigate, you should keep irrigating until the solution
coming out of your nose runs clear; i.e., all the gunk has been
completely flushed out of your nasal passages.  If 250 ml/nostril isn't
enough for that, then do more.    When I have a really nasty sinus
infection, I may need to use as much as 750 ml/nostril to get all the
gunk out with each session.

depends on how bad your sinusitis is

When just starting I irrigated 250ml per side at least twice a day. Now that
I'm doing much better I find 250ml total once a day an hour before bed is
enough to keep things in balance. You will have to find out what works best
for you but Steve L's advice about getting all the gunk out is certainly
correct if just starting to irrigate.  AW

Thanks for your replies everyone!

I have one more quick question:

At what speed setting should I put my WaterPik (lowest, highest, etc)?

Thanks.