can you tell me in each steps
not knowing where these people receive there knowledge,I can tell you that 1 1/2 pvc is 1 1/2 inside dia.and 2 inch pvc pipe is 2 inside diameter if you want to drill a hole for 2 pvc pipe make the hole 2 9/16 now this is sch.40 pvc pipe. sch 3034 is the same ID but uses different fittings because its thinner wall.Your going to have to know the astm number of the pipe to know anything about the actual size (thickness etc)
a copper pipe bushing is used to join two pieces of pipe that are different diameter's such as 3/4 and 1/2 pipe,normaly one uses the outside of the bushing to go inside the female end of a fitting and the insid of the bushing is drilled to accept the pipe itself. A coupler,or coupling is used in much the same way except it can be used to join 2 pieces of pipe of the same diamater or different diamaters and the pipe ends fit inside the coupling.
if the employer tried to accommodate your disability and you did not do your job then yes you can be fired
