Here's one: https://www.amazon.com/dp/B000O39QGW/Never heard of a pump assisted HOB overflow? I have a HOB overflow on one tank only pump im using on ghat tank is the returnpump and a aqualifter on the overflow and that only sucks air out of the overflowtube.
"We recomond the use of an Aqua Lifter pump with the CPR overflows for trouble free operation. Another alternative is to hook the bleed hose from the overflow to the air intake of a power head. This way the overflow will continue to wok if it drawes some air into it or in the event of a power failure it will restart"
I'm all ears if there's a cheaper alternative... stupid overflow box costs over half as much as the 135g tank did!