Copyright Goodheart-Willcox Co., Inc. 320 Section 3 Plumbing System Design and Installation sewer gas from escaping from the pipe once the build- ing drain is connected to the building sewer. The next task is to locate the sanitary tee to the kitchen sink in the stack, Figure 21-9. The height of the 2″ sanitary tee depends on the position of the 1 1/2″ 90° ell leading to the kitchen sink. The ell must be low enough for the horizontal pipe to run below the floor joists. In addition, the horizontal pipe must be installed with a fall of 1/4″ per foot of run. The following steps describe the procedure for completing this installation. Temporarily insert a length of 1 1/2″ pipe through the hole for the kitchen sink drain and put the 90° ell on the bottom end of this pipe. Position the 90° ell so that the open end is facing the stack and is at the correct height to allow the horizontal pipe that will extend to the stack to be secured to the underside of the floor joists. Mea- sure the distance A from the centerline of the 90° ell to the floor joist. For this example, assume that A = 1 1/2″. To calculate the height of the sanitary tee inlet, it is necessary to allow for a fall of 1/4″ per foot of run. See Figure 21-9, Calculating Fall insert. This means the cen- terline of the inlet to the sanitary tee should be 2 3/8″ (1 1/2″ + 7/8″) below the floor joist. Hold the sanitary tee 2 3/8″ below the floor joist and mark the 2″ pipe at the bottom of the fitting. Add the fitting allowance and cut the 2″ vertical pipe to length. Temporarily install the 2″ pipe and the sanitary tee. Measure distance B from the sanitary tee to the 90° ell and add the appropriate fitting allowances. Cut and test the fit of the pipe. The next step in installing the kitchen sink drain is to determine the length of the pipe from the 90° ell at the stub-out. Since a length of pipe is already in position, the rough-in height (assume 14 3/4″ above the sub- floor: 14″ rough-in + 3/4″ for the finished floor) can be marked directly on the pipe. Subtract the laying length of the 90° ell and cut the length of pipe. A short length of 1 1/2″ pipe and a cap will be needed to complete the stub-out. The pipe should be long enough that the stub-out will extend 3″ through the finished wall material. This will permit the cap to be cut off and an adapter installed during the finish stage of plumbing installation. Given the number of pieces that have been temporar- ily joined, permanently assembling these components will help keep everything in position while the stack is completed. The horizontal 1 1/2″ pipe will need to be secured to the floor frame near the 90° ell and the Fall @ ¼″ per foot of run: 3½uni2032 × ¼uni2033 per ft. = 7⁄8″ total fall 14¾uni2033 Mark centerline of 90° ell Mark here A 23⁄8uni2033 B 3uni2032-6uni2033 Floor joist Studs Sole plate Subfloor Blocking 90° ell Calculating Fall 2uni2033 pipe 1½uni2033 Goodheart-Willcox Publisher Figure 21-9. Locating drain for kitchen sink.