If you have an AM 1000 reactor, then open the air bleed valve on the top of the reactor. Attach some 3/16" airline to this and place the other end inside the suction side of the pump driving water through the reactor.

You can control the rate of purge by adjusting the bleed valve also.

You can also open up the reactor and on the inside, add some rigid airline tubing to set the intake lower down, say 3 cm deep, before the purge starts to work.

Regards,
Tom Barr