Choose the spot for the outdoor clothesline. Dig the first hole with the post hole digger. The hole should be two feet deep. Set one of the 4 by 4-inch boards in the hole. Back fill with the dirt dug out of the hole, packing the dirt down as you layer it in the hole.
Measure four feet off, holding the tape measure on the outside edge of the newly "planted" pole. Dig another hole for the second 4 by 4-inch board. Set the second 4 by 4-inch board in the hole and back fill with dirt, packing it down as you layer it in the hole.
Measure the distance for the length of the clothesline. Common distances are eight to 10 feet. Dig two more two-foot holes for the last two poles. "Plant" the poles as outlined in Steps 1 and 2.
Cut the 8-foot pressure-treated 2 by 4-inch board in half. Each half should be four feet long. Measure two inches in from one end on the 4-inch side of the board. Make a mark with a pencil. Measure two inches from the top of the board (to center the eye hook from top to bottom). This crossed mark will be where you drill for the eye hooks. Make the same measurements from the opposite end of the board.
Measure 14 inches in from the first eye hook and mark the board. Measure 14 inches in from the second eye hook and mark the board. Make the same measurements on the second half of the 2 by 4-inch board.
Use a proper size drill bit (this depends on the size eye hooks you purchased--they should be at least ¼-inch by 2 inches) to drill holes at the marks. Screw in the eye hooks, making sure they are all facing the same direction.
Hold the 4-foot board up to the posts. Using three screws for each post, screw the 4-foot board to the posts, making sure the eye hooks are facing the opposite set of posts. Repeat for the other end of the outdoor clothesline.
Thread the rope through one of the outside eye hooks. Tie the rope off with a good, tight knot. Run the rope lengthwise to the matching eye hook in the other set of posts. Run the end of the rope through that eye hook and pull it tight. Run the length of the clothesline to the third eye hook. Thread the rope through. Repeat until all eight eye hooks have rope running through them. Tie off the rope in the last eye hook with a good, strong knot.