Plumbing standards are set by the industry and are the same across the board. This includes dimensions for bathtub drains. This is true, however, for only the width of the pipes, drains and other fixtures. The length will vary, depending on what type of stopper you wish to use.
Bathtub drains are 1 1/2 inches wide and fit all standard bathtubs ranging from 14 to 26 inches deep. They are this size because they must fit the opening of the P-trap -- also 1 1/2 inches wide -- which is a special pipe that has a sharp bend in it. This bend traps water, creating a seal that blocks sewer gasses from traveling up the pipe and into the home. For this reason, bathtub drains are also sometimes called trip levers, trip waste drains or waste and overflow drains.
Bathtub drains usually include a built-in stopper, although this is not always the case. Rubber stoppers fit tightly over the drain and are not connected to the drain. Built-in stoppers are located underneath the drain. They are either operated by a lever located on the faucet or above the drain or operated by twisting and pulling on the drain itself. The length of this stopper varies depending on the type of drain and bathtub.
Appearance and Price
Bathtub drains are either brass or plastic. Brass drains are more durable than plastic but also cost more. The type of finish -- which is usually chosen to match the faucet -- also affects the price of the drain, as does the type of drain seal.
Location and Other Considerations
Bathtub drains are defined as left or right, meaning that they will appear on the left or right side as you are standing by the side of the tub and looking down at it. The drains are installed on the same side as the faucet. Shower drains are different from bathtub drains -- in fact, they are twice the size at 3 1/4 inches wide. They are also different from bathtub drains in that they fit an opening that is actually wider than the shower drain P-trap, which is only 2 inches wide.
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