a the washer 94 a seals the overflow fitting 60 a to the tub 18 in operation the drainage system comprising the ports 28 and 30 and pipes 34 36 and 38 are installed as shown in fig2 the vent pipe 40 and connecting pipe 42 are also installed in the conventional testing procedure the port 28 is plugged in any convenient manner the fitting 58 with diaphragm 64 is installed into drain pipe 34 as described above so there is no fluid access to the upper end of pipe 34 either inwardly or outwardly through overflow port 30 the vent pipe 40 is charged with water at some elevation above connecting pipe 42 so that the building inspectors can check to see if there are any leaks in the system having determined that there are no leaks the water is purged from the system the plumber can then approach overflow port 30 because cap 78 is not yet installed and by using knife 82 or the like cuts can be made in diaphragm 64 leaving a cutout portion 84 as shown in fig5 similarly in operation the overflow fitting 60 a is attached to the second vertical drain pipe 34 a already plugged by the diaphragm 80 a as described above so there is no fluid access to the upper end of second vertical drain pipe 34 a either inwardly or outwardly out of the overflow port 30 the vertical vent pipe 40 is charged with water at some elevation above connecting pipe 42 so that it can be determined if there are any leaks in the system with reference to fig1 having determined that there.