Re: snorkeing

There may be multiple things at work here.  First of all,
why is it harder to breathe through a long tube?  It isn't really
"harder", but what does happen is that the long tube has more volume
than a short tube.  So, after you exhale, more CO2 is left in the
long tube, which you then breathe back in causing you to get less
fresh air.  A similar thing may be at work when you try to clear
the water from a longer tube.  In order to get the water out, you
need to be able to replace it with air from your lungs, and to first
order this means the volume of air in your lungs would have to be
greater than the volume of water in the tube.  More subtlely, the
weight of the water increases the pressure of the air in the tube,
which even further decreases it's volume.  Also you would have to
be able to exert enough pressure with your lungs to force the water
upward (assuming the tube if vertical).  At some point, the water
will be too heavy for you to push out with your lungs alone.