Injecting CO2 into pump?

I have read numerous ways of dissolving CO2 into the water including using glass diffuser,flipper and CO2 reactors. I know glass diffuser or flipper not as effective as reactors.
One bro told me he injects CO2 directly into his Eheim filter. Seems logical. However, i am using an overhead filter and think of just letting the CO2 being stuck into the pump head.
Can someone share his experience if this method has worked? Thanks.