Here you’ll find a  helpful explanation of how a bathtub works, with common tub types, styles and sizes, with bathtub drain plumbing diagrams

Man installing water supply lines to bathtub valves.
A bathtub’s valve is connected to water supply lines, and the drain connects to the home’s drain line. With a whirlpool tub, electrical power is needed to operate the pump. Kurhan /

Bathtubs may be either built into a three-wall alcove or freestanding.

Built-in tubs range from familiar tub/shower combinations to ultra-modern, computerized whirlpool tubs that automatically deliver and maintain a given water temperature.

A conventional small bathroom with a white alcove tub shower.
Conventional 5-foot bathtub is designed to be inset into an alcove. Iriana Shiyan /

Freestanding tubs come in many styles, too, from classic claw-footed tubs to elegantly sleek, jetted models.

Bathroom with an enclosed glass shower area beside a freestanding tub.
Large freestanding bathtub offers the ultimate in luxury. Iriana Shiyan /


Beach view bathroom with a drop-in tub, including a greenhouse window.
Drop-in bathtub mounts in a step-up platform. Iriana Shiyan /

The best bathtubs are made from enameled cast iron. Though they’re incredibly heavy, particularly in large sizes, cast-iron tubs have deep, durable finishes.

Tubs made from fiberglass-reinforced acrylic are also good, and, because they are considerably lighter and more easily molded, they tend to come in larger, more intricate styles than cast-iron types. Some tubs are also made of fiberglass, but these tend to fade in direct sunlight and scratch a little too easily.

The conventional length of a bathtub is 5 feet, but tubs are made up to 7 feet long. A wide range of widths and depths is available.

Bathtubs that include a shower have a diverter valve that switches the flow of water from the tub spout to the shower head. Here is how the setup works.

Diagram of a shower plumbing with a diverter valve, including water flow control variations.
Plumbing Diagram © Don Vandervort, HomeTips

Bathtub drains have two legs, one to the main drain opening and the other to the overflow drain opening. To close and open the drain, two different assemblies are common: pop-up and plunger-type. Both are operated by a trip lever at the overflow drain.

With a pop-up drain, linkage forces the drain stopper up or down by way of a rocker arm. With the plunger type, a hollow brass plunger slides up and down inside the drain assembly to seal the drain opening. For more about pop-up stoppers, see How a Pop-Up Drain Stopper Works.

Diagram of two types of bathtub drainage systems, including pop-up, plunger, and its parts.
Bathtub Pop-up Diagram
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About Don Vandervort
Don Vandervort has developed his expertise for more than 30 years as a remodeler and builder, Building Editor for Sunset Books, Senior Editor at Home Magazine, author of more than 30 home improvement books, and writer of countless magazine articles. He appeared for 3 seasons on HGTV’s “The Fix,” and served as MSN’s home expert for several years. Don founded HomeTips in 1996. Read more about Don Vandervort