What type of knot is commonly used for a tag line?

The clove hitch is commonly used for a tag line because it creates a secure and adjustable attachment that is easy to tie and untie. This knot is particularly useful in various rigging and hauling applications, serving as a reliable means of securing a rope to a post, rail, or any fixed structure. Its structure allows it to hold firmly under load while being easy to adjust, making it ideal for managing tag lines in plumbing installations or other scenarios where quick adjustments may be necessary.

In contrast, the figure-eight knot is primarily known for its role in climbing and is often used to create a strong loop at the end of a rope, but it's less adaptable for attachment to fixed points. The square knot is designed for tying two ends of a rope together and isn't ideal for securing a line to an object. Lastly, the bowline knot creates a fixed loop at the end of a rope, which is also not intended for attaching to objects like poles or posts, making the clove hitch the most suitable choice for use as a tag line.