DIY Network

How to Finish the Plumbing for a Tub/Shower Unit

DIY experts show how to complete the plumbing hookups for a fiberglass tub and shower installation. Low-maintenance tub and shower surrounds are suitable for new construction and some renovations.

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  • Time


  • Price Range

    $100 - $250

  • Difficulty



Step 1: Connect the Main Water Supply

In our project, we've already connected the drain assembly after installing the shower/tub unit with spout and diverter assembly. We're now ready to finish the plumbing installation.

Make sure the main water supply is turned off. Remove any caps from the ends of the water lines. If the caps are soldered in place, heat them with a blow torch and pull them off.

Cut as many pieces of pipe as necessary to install the water supply lines to the sides of the diverter unit. Be sure you attach the lines to the appropriate fittings. For copper piping, connect the pieces of pipe by "sweating" them into place: soldering using a blow torch after wiping ends with an Emery cloth and applying copper flux. Or, for copper or other piping, use compression fittings.

Install the shower riser pipe from the top of the diverter. Follow any manufacturer's instructions that are included with the fixtures and assembly. Secure the top of the shower riser to a support block placed between two wall studs.

Complete the installation of any other plumbing fixtures necessary to finish your shower/tub enclosure, following manufacturer's instructions.

Step 2: Finish P-Trap Installation

From underneath the tub, dry-fit the P-trap assembly to make sure everything will fit properly. Install the brass adapter fitting to the drain tailpiece and loosely connect the brass adapter to the bottom of the tub.

Install the P-trap onto the drain tailpiece.

Attach a horizontal pipe to the P-trap and fit the other end of the pipe to the main drain line. You may need to use a reduction fitting for a proper connection.

Once you're sure the P-trap assembly will fit, complete the installation using PVC cement. Apply the cement by sparingly smearing it around the surfaces to be connected. Press the fitting together, give it a half-turn, and hold it for about 25 to 30 seconds.

Finish any plumbing or faucet connections not made earlier and reconnect the water supply to check all fittings and operation of the faucet, diverter and showerhead.

Step 3: Finish the Surround Enclosure

To finish the new shower/tub unit, install water-resistant drywall around the enclosure. You will need to install 1/4" shims on the studs closest to the tub to compensate for the thickness of the fiberglass flange.