I'll help if someone will tell me what "IIRC" means (I keep seeing this and, while I'm sure it will be obvious once it's spelled out, I have no clue at this time)

This sounds like it's 'in-line' (like the CL200 - the CL220 has little hoses to feed it and put the chlorinated water into the return stream). I wouldn't sweat the back pressure from it - most of the water bypasses the chlorinator, though there is some restriction in the pipe. Use unions to connect it!!!! Please don't just throw a couple of male adapters into the unit - use the outer threads for the unions (for the CL200 the proper unions are the SP1500-UN-Pak).

If you're at the max for what your system will stand for back pressure, you can use 2 tees, 2 90*s and 2 unions to install the feeder parallel to the return pipe, you won't get as much flow through the unit, but you can compensate by turning up the feed dial on it.