Using the post hole digger or shovel, dig two holes approximately two feet deep. Space the holes as far apart as you would like the length of your finished clothesline to be.
Insert an 8-foot post into the first hole. Have your helper hold the post steady and level while you mix the Quikrete and water. While your helper is still holding the post level, pour enough Quikrete into the hole to fill it half full. Allow the Quikrete to cure for the time indicated on the packaging. Once finished, fill the rest of the hole with dirt.
Proceed to the second hole, repeating the process as outlined in Step 2.
Wrap one end of the rope, nylon cord or heavy twine around the top of the first post once, starting about six inches from the end, and secure it with a knot. Wrap it around two or three more times, tying it off with a knot at the final wrap.
Pull the rope or cord taut, stretching it across to the other post. Make sure there is no slack in the rope between the posts because this will make the clothesline sag. Wrap the cord around the second post once and tie it off in a knot. Continue to wrap the cord two or three more times around the second post, tying it off in a knot after the final wrap. Cut the excess cord, leaving 2 to 3 inches.