Main drain fixture question

[ConcreteChris]

Getting ready to put in fixtures in to rebar.. (skimmers, main drain)... In the engineered plans the main drain calls for a 4" tunk.. The plans also spec out two main drains called
" Lawson aquatic 9 super-sump vgb certified" anyway the port where is connects is a 4" connection but not open. It is sealed with only looks like a 1/2 treaded hole with a cap screwed in....... My question is, do i cut the 4" hole open before gluing on? Why a 4" line when the feed hole is only 1/2".. any help would be great,

 

[Texas Splash]

@mas985 are you familiar with this drain set-up?

 

[mas985]

I have never had any experience with that one but I suspect the 4" plug pops out if you put a 1/2" pipe in the center and pry it out (i.e. pop out). Also, I would think you want to do that before attaching the pipe.

@jimmythegreek may know for sure.

 

[ConcreteChris]

I have never had any experience with that one but I suspect the 4" plug pops out if you put a 1/2" pipe in the center and pry it out (i.e. pop out). Also, I would think you want to do that before attaching the pipe.

@jimmythegreek may know for sure.

It definitely doesnt "pop" out i would have to drill it... Im attaching a couple actually photos