Copyright Goodheart-Willcox Co., Inc. Chapter 21 DWV Pipe and Fitting Installation 327 The double wye can be located anywhere between the 90° ell and the double sanitary tee. For this exam- ple, the midpoint was chosen. To determine the length of the 2 1/2″ and 2″ lengths of pipe, subtract the over- all length of the fitting from the 3′ distance between the double sanitary tee and the double sanitary wye and di- vide by two. Add the appropriate fitting allowances to determine the correct length of each pipe. The pipes and fittings that extend from the double wye to the bathtubs can then be installed. The key is to locate the 1 1/2″ 45° ell. Begin by temporarily insert- ing a length of 1 1/2″ pipe in the double wye and sup- porting it below the floor joist. Identify which part of the structure the 1 1/2″ pipe to the bathtub P-trap will be parallel to. Typically, this pipe will be parallel to a foundation wall, and it may be parallel to a floor joist. Measure the distance (A) from the parallel surface to the point where the 1 1/2″ pipe connects with the P-trap, Figure 21-23. Once this measurement is transferred to the 1 1/2″ pipe (B), the laying length of the fitting is subtracted and the pipe can be cut to fit. Measure the length of pipe from the ell to the P-trap. Add the appro- priate fitting allowance and cut the pipe. Procedures for installing the remainder of the pipe and fittings for the bath stack are the same as those de- scribed previously for the kitchen/laundry stack. Once the DWV piping is installed, it is necessary to close all openings either with caps, plugs, or test plugs so that the system can be tested. These procedures are dis- cussed near the end of Chapter 23. 2 × 1½ × 1¼ × 1¼ double sanitary tee Level to check plumb Length of 2° pipe 36° 23⁄8° fall 33⁄8″ 2½ × 2 × 1½ × 1½ double wye Wall between lavatories and tubs Vent thru roof 1½° vent can also be installed Mark here and add fitting allowance to determine length of pipe. 1″ A B 3uni2032 Goodheart-Willcox Publisher Figure 21-22. Installing the 90° ell and double sanitary wye requires calculating the fall for the horizontal portion of this run of pipe.