catchment tank overflowing the top

[terracore]

Well the mystery deepens... when I took the cover off the water had dropped to the normal level and the tank was no longer overflowing. I couldn't tell that there was any air in the overflow thing but I followed the instructions and spun it around 100 different directions while underwater and put it back. Will have to wait for the next big rain to find out if its working correctly.

ETA: Another component of the "mystery" is that we've had rains a LOT more severe than yesterday... so not sure why it happened this time.

Thanks everybody for their help!