Overflow box not siphoning

[wetcoast]

Yes looks very similar to that.

I have taken the box right off and attempted to start the siphon all over again with no such luck. It doesn't LOOK like there are any leaks or holes in the acrylic and I can hear a sucking sound when the hose is attached to the top nipple of the box to suck air out.

I think I may be able to get a utube type box today for testing and will see how it goes - but the fact of the matter is - this doesn't make any sense at all - It wont even start sucking from the "inside of tank" part of the box

.. and everything was going so good lately..