In rigging terminology, a pulley has a groove flanked by two flanges. The groove is what the rope bears on. On a Gray-B-Gon, the groove is a 1" length of PVC pipe with a nonskid surface, and the flanges are plastic container bottoms.
Clean the surface of the PVC pipe length with a paper towel and alcohol, and let it dry on a clean, flat surface. Measure and cut a 5-1/4" length of anti-slip tape. Peel about 1" of the backing and fold it back. Avoid letting the adhesive touch anything.
Place the tape on edge beside the 1" pipe. Success now depends on avoiding accidental contact with the adhesive, and on keeping the tape edge in light contact with the flat surface, for alignment.
Press the folded backing against the pipe, then slide your finger toward the exposed tape end. Once the tape end sticks, pull the loose end of the backing to expose more adhesive. Press this exposed adhesive against the pipe, rotate and repeat. When it's fully mounted, you should see a gap of about 1/32".
You will find ideal flanges in your grocery store: deli tubs, with rounded walls, that once contained olives or other delicacies. Look for an eight-ounce tub; deeper tubs must be cut down, which sacrifices strength. Don't use tubs with straight walls that extend below the bottom to form a strengthening ridge. The rounded wall defeats the drive belt's attempts to climb off the flange.
Tubs made of "PETE" (polyethylene terephthalate, icon "1" in the recycle triangle) look flimsy but resist weathering and UV. Tubs made of polypropylene ("PP", icon "5") look almost identical but shatter easily. Avoid containers with irregular or deeply lobed floors.
First cut a 1-3/8" hole in the center of the tub's floor with a fine-tooth hole saw. Don't worry if the hole isn't precisely centered. If you've got an 8-oz tub, you're finished. If you have a deeper (16, 24, or 32 oz) tub, cut the walls down to 5/8": hold a marking pen against the tub at 5/8" while you rotate it, then cut as evenly as possible.