[LazyPup]

If you examine the interior of a common PVC coupling you will see a raised ring on the interior in the center of the coupling. That ring is a stop to insure that each pipe is only inserted 1/2 way into the coupling.

The coupling that you are describing as a "Fix it" coupling in most likely a "Repair Coupling" which has no internal stop ring.

To make a repair in close quarters where you cannot move the pipes you begin by cutting out the defective section of pipe. The section that you cut out should be at least 6" long and make sure that the ends of the pipe are cut square.

You next cut a section of new pipe to replace the cutout section. The section of new pipe should be cut about 1/4" shorter than the distance between the open ends of the cut out section.

You then slide either the repair coupling or the compression coupling completely onto either one end of the existing pipe or on the replacement pipe, whichever is more convenient. Slide it far enough onto the pipe so the end of the pipe is exposed for cleaning.

Next use your solvent/cleaner to clean both ends of the repair pipe and both ends of the existing pipe.

Now you use a common coupling to glue the repair section to one end of the existing pipe, the opposite end of the repair pipe should now be aligned with the other existing pipe for form a tight butt connection. You eihter apply glue and slide the repair coupling over the joint, of if you are using a compression coupling you slide the coupling over the joint and tighten it in place.