Attach an external mounting cap 2 inches from each corner on the bottom of the butcher block table top. Mark the holes with a pencil and predrill the holes. Screw the caps to the bottom of the table top.
Assemble the four legs. Brush PVC cement into the top and bottom connectors of a four-way tee. Insert 20-inch sections of PVC pipe into the top and bottom of the tee. Press them together firmly and allow them to dry according to the PVC cement manufacturer's instructions. Repeat for the other three legs.
Arrange the four legs in a rectangle with the horizontal connectors facing each other. Brush PVC cement into each of the connectors. Insert the 40-inch PVC pipe into the horizontal connectors, parallel from each other. Quickly insert the 18-inch PVC pipe into the other side of the connectors to complete the rectangular base.
Turn the countertop upside down. Brush PVC cement into the external mounting caps. Quickly press the four legs into the mounting caps. Allow it to dry completely.
Add a PVC cap to the bottom of each leg. Glue it with PVC cement and allow it to dry before turning the table right-side up.
Wipe the butcher block with food-grade mineral oil. Allow the oil to absorb into the wood and repeat. Generally a butcher block requires four to six coats of oil. Remove any excess oil with a rag and buff the table top to a sheen.