this is the tailpiece you want. you will need a 1.5" hole saw.
a 3.5 gal bucket filled to 7" is 2.5 gals.
the turface bags are 1.5 cu ft and so is approx 11.25 gals so you can fill approx 4.5 buckets to the 2.5 gal level. this is unscreened and uncut.
the big bags of chunky perlite are 4 cu ft so if you were to mix 3 bags of turface with one bag of perlite you would be about right.
you would end up with approx 8 cu ft of material so about 60 gals which should be enough for approx 24 containers.
it won't come out exactly as you might think because of the way the particles of each fit together but it will be real close.
i would not screen the turface but wash the hell out of it separately from the perlite. a big tub and a hoe are useful.
the perlite is best cleaned by floating it in a large tub and letting the fines go to the bottom. then use a net to scoop out the floating perlite.
the perlite will also need a 1000 ppm or ec 2 bath at the same time you clean it.
wash them separately and then mix them wet.
you will need plastic vent screen from lowes for the end of the tailpieces. it has a larger mesh than window screen and doesn't clog as readily.
i would use a 2.5" hole saw for the lid of the bottom container.
i attach the vent screen with a nylon cable tie about 3/8" from the end and then run a bead of glue around the top of the cable tie. it will never slip off.
amazing goop plumbers edition is the glue. it can also be used to glue the tailpiece to the bucket if you like.