Slow sand filter storage container: More info on Filter 4  The
water clarity of the output from filter 4 has been getting worse
and worse up until 2 days ago. An air vent on the top of the
barrel was added after I noticed the output pulsing while the
pump was in operation. I realized at that time that the pump was
actually drawing water from the filter’s output because the
water had reached the top of the barrel beyond the overflow
drain just below the top and was forming a seal so as to allow
the pump drawing water to create a vacuum strong enough to
briefly cause water to be forcefully drawn through the filter
much faster than it could handle. This was (apparently) causing
the increased turbidity and (possibly) the biological
contamination of the output water. So. . . know that:  The
storage container, especially when used with a pump, must be
vented above the water level in the container or the pumping
action from the small recirculation motor  (or any pumping
action) will actually forcefully draw water fr