Try creating a more direct line to the sump from the hose underneath.
If hose is bent or curled slightly upwards before it flows down to the
sump it could be filling with water until there's enough to to flush.
Also make sure drain in overflow is not slighly plugged with debris
.....


D P wrote:
Did you try to Manually add more water in the filter, untill the flow is
smooth?

"Shassmom3" wrote in message
.. .

I have a 120 gallon tank with two built in overflows. One side seems to
work fine and the other side makes a flushing sound. The water level in
that column drains down and then fills back up. Is there anything I can
do to fix this problem?




--
Shassmom3