Bleach I understand and as far as blowing out any residual bleach why not just hook it back up to the CO2 and let that run outside the tank for a few minutes. I've found hydrogen peroxide and vinegar work well for my diffusers.
I would prefer a reactor to an in tank diffuser just for aesthetics. After using an in tank diffuser for the past couple of years I can't take all the bubbles any more and have gone to in inline diffuser on the input of one of my canisters. Contrary to popular opinion, there have been no airlocks, burping, failed gaskets, ammonia spikes due to killing off my biofilter, etc. and the RCS that inhabit the filter are still happy and multiplying just like before.