DIY CJ Mega Standpipe 2"

 

I can't identify the "collar" part of the standpipe. It looks like a 4" to 2" adaptor of some kind, but I can't find one locally. Also, I'm not sure how the water flows into the pipe.  There's a picture there that looks like they took crescent-shaped slices out of both sides of the pipe, leaving enough material to glue the collar and cap to. 

Has anyone tried to make one of these?  I need something that has a smaller footprint than the durso design, but allows for a 2" drain.