Why water goes into a pipe by turning in one direction only?

Question

Why water goes into a pipe by turning in one direction only?

Answer 1

When you s***w the tap on, it moves upwards slightly, as a s***w valve is moving up inside a pipe, and letting the water through, when you s***w the tap off, the s***w valve closes.

Yes it could be made the other way, certain fire equipment is made this way.

EDIT: If your inquiring about the draining effect, yes this does have to do with whether you live in the northern or southern hemisphere (the rotation of the earth) apparently it is more noticeable in the northern hemisphere, specifically America (i've been told this is because the toilet bowls are alot bigger)

Answer 2

I believe it has to do with the spinning of the earth.  It is also different in the northern hemisphere and southern hemisphere.