To connect the 1/2 PVC (input , output) i use saw hole (i will post the size, is at work) NEVER use regular (large) drill , even if is 1/4 thick, huge chance to crack, broke the Acrylic Tube (reactor) regular drill will cut w/only two points (flute) then very hard to hold the reactor or drill gun to avoid vibration . Saw hole use 30-40 teethes in same time , a way less aggressive than dill.
To seal the hole , i fond this (see the pics) in Home Depot , electrical dept. , very important to use some kind of lube, to avoid shoveling, shave the rubber when you install or connect the pipe , i use honey, same when service my Protein Skimmer, ATB have a trike "O" ring, if force , big chance to pinch the rubber.After install the rubber seal into reactor i suggest to lock (glue around by using ice-gel ) you will shave the seal , around rough hole from saw hole. In my case i use 4.750 inch (4 3/4) food bowl from Crate & Barrel $ 3.40 is made from nice "porcelain" material , i have to shave just 1/16 of the inch (0.62) so like 1/32 per radius , that was the most difficult to make, that material is very hard, i screw one by the time i find the right operation (i use tile diamond cutting machine, i keep rotate the bowl against side of the Diamond disc, until i got my sweet size, i would NOT suggest this, huge chance to cut your fingers , so try to find a Tube ,Reactor that have 4 3/4 ID , or try to visit Crate & Barrel for dif. size , they have. The main key is to use this bowl to help to move Bio-Pellets by using less energy (power of Gal/H pump) concave shape of the bowl help to move UP and Down very easy, surface of the bowl is so smooth work just like ramp, imagine how hard is to move one big wheel, after spin is so easy to maintain the move, same here. In my opinion the biggest efficiency is when move very gentile the pellets, avoid bang or aggressive move.