I DON'T KNOW WHERE THE SAYING CAME FROM THAT U CAN'T SEE PVC BUT ONLY AIR IN IT,I POSTED SOME PICS ON HERE 2YEARS AGO OF EVERY PIPE ON THE PVC .IT HAD BEEN THERE A LONG TIME . ALSO SOME SAY ONLY SEE AIR BLATTER ON FISH BUT THAT IS NOT SO EITHER BECAUSE ON BIG FISH U CAN SEE THE SHAPE OF THE FISH AND NOT HIS BLATTER