Ok, a jumble of who knows what going on here.... hope to clarify a bit.
PVC and acrylic are not typically glued together, maybe he misread.
Toilet flange/closet flange not cool, and typically ABS. They are meant to be knocked out when done and rarely available in 6". If available in 6" PVC make sure it's not the knockout type.
a simple sheet of 1/4" -1/2" pvc, square, or round will do.
Solvent or heat weld it on, and it will form a permanent watertight bond