here's how i made mine. its based off the rex design, just a few differences...
here's what i did. here you can see a pic of the fitting where the co2 line will be attached to
this makes for a clean design, but the problem is, as stated, that by insterting the co2 at the edge of the pvc piping, the co2 bubbles will have a tendency to run along the side of the pipe, avoiding the incoming water and will not get dissolved proplerly. so, what i did was add another fitting on the inside of the pvc fitting. thing is, you cant thread a fitting in from the inside. SO, i filed down the threads from the inside and forced in the plastic fitting you see here (1/4" barbed fitting).
this fitting is fitted with a piece of rigid plastic tubing that stops about halfway into the tee. here you can see the reducer fitting with barb fitting placed into the tee connector. the co2 will exit in the middle of the reactor and meet the incoming water to get dissolved effectively.
to avoid any leaks, i sealed the whole inside of the reducer fitting with silicone
here's a pic of the tee connector with the reducer fitting and the barbed connectors
and here's the completed assembly, in the cabinet.