Measure the inside of one of the elbows from the lip of one of the holes to the butt ridge This determines the distance a pipe slides in to the fitting. Multiply the measurement by two. Cut three pieces of pipe at that length. Coat the outside of half of each of the pieces and both openings of the 180-degree elbow. Coat the primered portions of both pieces and the elbow fitting. Insert the pieces into the holes in the elbow. Hold the pieces in place for a 10 count. If you do not, the pieces back out of the fitting.
Primer and glue one of the pieces protruding from the 180-degree elbow as well as one of the holes in the 90-degree elbow. Slide the elbow over the piece of pipe. Twist the 90-degree elbow until it is parallel with the 180-degree elbow. Hold it in place for a count of 10. If the 90-degree elbow is offset to one side or another, it will not line up with the pipe from the condensation pan.
Primer and glue the other piece of pipe protruding from the 180-degree elbow as well as one of the arm holes of the T, not the leg hole. Slide the T over the piece of pipe and twist the T until the leg hole is parallel to the hole in the 90-degree elbow. The trap construction is as follows: 90-degree elbow, piece of pipe, 180-degree elbow, piece of pipe, T. The open hole from the T leg and the open 90-degree elbow hole are in line with one another.
Slide the last piece of pipe into the second arm hole of the T after each are primered and glued. Slide the cap over the other end of the piece of pipe -- without primer and glue. It must remain removable.
Primer and glue the PVC pipe running from the condensation pan and the open hole of the 90-degree elbow. Slide the elbow over the pipe and hold it in place. Primer and glue the PVC pipe from the coil of the air conditioning unit as well as the leg hole of the T. Slide the T over the pipe and hold it in place. The 180-degree elbow belongs on the bottom of this arrangement, the removable cap facing up.