PVC fittings are mass produced creating an economical product and a wide variety of choices, but also numerous problems. With so many fittings and pipes being manufactured there become issues with standardization and quality control. The frustration of fittings which are too tight, too loose, or leaky fittings can create issues with seemingly simple projects. Many of these issues can be quickly and easily fixed creating a lasting solution.
Often if a fitting is too tight, the correct diameter might not have been purchased. Double check the diameter on not only the fitting, but also the pipes being fitted. If the diameter is correct, carefully use a utility knife to bevel the edges of the fitting. Do not cut away too much of the plastic and weaken the connection, merely be sure to scrape any excess plastic which could be obstructing the fit. After beveling, test the connection again. If the fitting is still too tight, use ultra fine grit (200+) sandpaper to sand the PVC pipe which is being fitted. After sanding down the pipe, be sure to remove any plastic dust or debris with a damp cloth before connecting.
A fitting which is too lose can often result in slow leaks, annoying drips, and otherwise dangerous pressure to be released. To fix loose connections first it must be determined if the fitting is threaded or not. Threaded connections should be dealt with carefully as the threads themselves taper in width and extra bulk between the two pipes can cause excessive pressure and cracking. Never use Teflon or plumbing tape on threaded PVC pipes. Plumbing and Teflon tape were intended as lubricant for metal piping and can increase pressure strain on the threads causing cracks. Instead, use an extra thick layer of PVC cement and coat the connection with PVC sealant. This will preserve the threads internally, but stop any leaking air or water externally.
For non-threaded fittings, Teflon tape can do a great deal to slightly increase the diameter of the pipe, but still provide a substance which will not degrade with water or heat. Wrap the Teflon or plumbing tape around the male end of either the pipe or the fitting 3 to 4 times and test fit. If added tape is needed, another 3 rounds can be added. When using Teflon and plumbing tape the fitting should end up being quite snug, so use firm pressure.
Leaking PVC fittings often comes from a break down of the internal threads within the fitting. Since the threads on PVC become slightly thicker as the fitting is screwed on, it is easy to add undue strain on the smaller threads in the beginning. As the threads are forced, they crack and can become leaky. The same is true for fittings which begin to leak over time if they have been screwed on too tightly. As the pressure increases within the pipe, the threads which are already experiencing too much stress begin to split. To keep from splitting the thinner threads, never over torque the fittings more than one to two turns past fingertip tight.