Make square cuts for strong joints
Square pipe ends fit snugly into the fittings, allowing plenty of contact area for the solvent cement to work. They also make a smoother interior surface for better water flow. A power miter saw and other special tube cutters guarantee square cuts, but you don't have to buy them. You can do a good job with just a handsaw and an improvised guide. The photo shows an easy-to-use guide that's made by screwing together scraps of 2x4.
For the best results, use a saw with fine teeth and a blade that's 3 or 4 in. wide. A hacksaw is a poor choice because the narrow blade tends to wander easily. Special saws for cutting plastic pipe are a worthwhile investment if you do much plumbing work. You'll find them in the plumbing tool area or with the handsaws in most home centers and hardware stores. Otherwise, any fine tooth saw will work.
Sand off the saw burrs for a better fit
Plastic burrs left from sawing can cause trouble. Outside the pipe they'll interfere with a good fit. On the inside they can collect debris and slow the water flow. You can remove them with a file or pocketknife, but sandpaper is easier to use and works great. Simply roll a quarter sheet of 80-grit sandpaper into a tube and flatten it slightly to match the curve of the pipe. Then hold the sandpaper at an angle and sand the inside and outside of the plastic pipe until you create slightly beveled edges.
Mark the pipe and fitting for precise orientation
By the time you spread the solvent cement on both the pipe and the fitting and press them together, you have only several seconds to get the alignment right before the pieces are stuck together. That's why it's a good idea to make alignment marks beforehand on joints where orientation is critical. Dry-fit the pipe and fitting, using a torpedo level if needed to align the fitting, and make a mark across the fitting and pipe. Use these marks to align the fitting and pipe when you join them with solvent cement.
Push and twist for leak-proof joints
Just swiping the pipe with cement and pushing on the fitting won't ensure a strong joint. You want to make sure you have an even layer of cement over all mating surfaces.
If you're using PVC or CPVC pipe, wipe primer around the pipe and into the fitting to prepare it for the solvent cement. Let it dry about 10 seconds. Then spread an even layer of solvent cement on the same surfaces. To keep excess solvent cement from being pushed into water piping, don't apply too much to the inside of the socket on the fitting. At this point you have to work fast to complete the assembly. Align the fitting and pipe about a quarter turn from their final orientation. Then twist the fitting a quarter turn as you press it onto the pipe. Twisting the fitting helps spread the solvent cement evenly to ensure a solid joint. If you've made alignment marks, make sure they're aligned with each other. Hold the pipe and fitting together for about 15 seconds until the cement grabs. If you let go immediately, the pipe may push out of the fitting, resulting in a weak joint.
The solvent vapors from the primer and cement can make you dizzy and are dangerous to your health. Make sure you have plenty of ventilation or wear an approved organic vapor respirator when working with primer and solvent cement.
Fix mistakes with a coupling
It's always a bummer to make a mistake. But at least with plastic pipe it's easy to fix. Simply saw out the messed up section, whether it's too long, too short or crooked. Correct the mistake and reassemble the joint with a coupling. In some cases, you can reuse the old section of pipe and fitting. Otherwise, set it aside and cut new parts. You may be able to use the bad section later.
Tip: Buy extra fittings. Having extras on hand will save a trip to the store. And you can return the extras when you're done.
Allow for shrinkage if you dry-fit the pipes
Most novice pipe fitters find it reassuring to cut and assemble a group of pipes and fittings before gluing them together. It's OK to do this as long as you're aware of the pitfalls.
Don't jam the pipe and fitting together too tight. They'll get stuck and can be difficult to get apart. If a fitting does get stuck, just set a block of wood against the lip and pound the fitting loose with a hammer.
Leaving the fittings loose keeps them from getting stuck, but it creates another problem. You can't assume that the final assembly will be the same size as the dry-fit parts. When you apply solvent cement to the pipe and fitting and press them together, you'll lose a little length at each joint. On 1-1/2 in. pipes, this could be as much as 3/8 in. per joint. So keep this in mind if you dry-fit, and allow extra length where fit is crucial.
Another tip is to limit dry fitting to a small group of pipes and fittings. Join this group with solvent cement before moving to the next section.
Use the proper solvent for each type of plastic
There are three common types of plastic plumbing pipe: PVC, CPVC and ABS. Each requires a different kind of solvent cement. The white or beige pipes (PVC and CPVC) also require a primer. You don't need a primer with black ABS pipe. Read the label to match the solvent cement to the type of pipe you're using. Avoid universal solvent cements.
Use transition couplings to connect different types of pipes
Transition couplings have a flexible rubber sleeve surrounded by a metal sleeve and band clamps. They're handy for connecting plastic pipe to cast iron, copper or steel, especially if you can't thread on an adapter. Each coupling is labeled with all the different types and sizes of pipes it can join. Home centers and hardware stores keep a few common types on hand. Read the label on the transition coupling to find out which pipe it joins. For less-common connections, contact a local plumbing supplier or ask about ordering a special transition coupling. Rubber couplings without the metal sleeve often aren't code approved. Ask your local inspector if you're not sure.
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Video: How to Glue PVC Pipe
Gary Wentz, an editor for The Family Handyman, will show you how to glue PVC joints to get a fast, leak-free seal.