Put the water in the tube BEFORE you hook it up to the fitting on the
manifold.  If you try to fill the tube with one end closed at the manifold
it takes longer.  When filling watch to see that the water doesn't go higher
than say 6" above ground level so as not to put any into the manifold
itself.  All the water should be in the tube.

Obvious if you've done it once but not so if you haven't.