In previous articles in our series on PVC plumbing for aquariums we reviewed the various components you can use to design your own water distribution system. In this installment we‘ll explain how to properly cut and assemble PVC pipe and components for a reliable leak-free plumbing system.

Tools for Assembling PVC

You will need the following tools to construct your PVC plumbing system:

tools to have that help assemble pvc

  • A tape measure and marker are essential for measuring fittings and pipe. There is no way to accurately “eye-ball” it and make the proper calculations.
  • A hacksaw is the most common way to cut PVC pipe. If you’ll be making a lot of cuts, a PVC cutter tool is recommended. This specialty tool looks like a pair of pliers with a very sharp, thick blade fitted on one side. Just position the pipe in the cutter and squeeze the handle.
  • PVC primer and glue. We’ll talk more about these later.

How to Properly Measure PVC Pipe

example of the inside lip of a pvc fitting that stops pipes from being inserted too deep

When measuring a length of PVC pipe for attachment to a fitting or valve you must include the depth of the fitting. The pipe must completely enter the fitting and seat correctly into the socket. Look inside a PVC elbow or other fitting. You’ll see an inside lip that prevents the pipe from going in farther. Use a tape measure to determine how much pipe is needed to slide completely into the fitting until it is stopped by the lip. Do not attempt to push the pipe into the fitting to get the measurement. Many PVC fittings are slightly tapered and won’t allow you, in most cases, to fully seat “dry” pipe. We’ll explain this in detail when we get into how to glue PVC. The take-away is to use the tape measure to calculate the depth of the fitting.

How to Cut PVC

The most-common way to cut PVC pipe is with a hack saw. A hack saw blade is designed for cutting metal. The fine-tooth blade has forward-pointing teeth so cuts on the down-stroke. A hacksaw blade will make a smooth cut across PVC pipe.

  • Mark the pipe where you want to cut. Make sure the line is perpendicular to the length of pipe. The cut should be square, not on an angle. A square cut makes a good seal inside fittings.
  • Hold the pipe securely against a flat surface so it does not move around while you use the saw.
  • Make slow, smooth strokes with the saw. This will prevent chipping on the end of the pipe. As the pros say “Let the saw do the work.”

Mentioned earlier, pipe cutters are a popular choice when making multiple cuts. They will save time and make less of a mess than a hacksaw.

Remove the Burrs!

When you cut PVC with a hacksaw it leaves a rough edge with burrs. The burrs are small pieces of PVC that are loosely attached to the end of the pipe.  The burrs will make it impossible to slide the pipe into a valve or fitting. Burrs left inside the pipe will eventually pass into the aquarium, protein skimmer or contactor. There are two ways to remove burrs.

during pipe cutting, the process can create rough edges which need to be cleaned up

  • Using a sharp blade, like a box cutter, run the blade around the outer and inner edge of the pipe. Hold the blade on an angle for a smooth pass.
  • Use fine-grade (120 grit) sandpaper to gently brush away burrs on the inner and outer rim of the pipe. Don’t aggressively sand the pipe. It could rub too much PVC off the pipe and cause a poor fit inside valves and fittings.

Test Fitting the PVC Components

"Dry fitting" is when you assemble the PVC system without glue. The problem is many PVC fittings are designed to connect to pipe by friction fit. This means the fitting is slightly tapered to make an extremely snug fit, so there’s no gaps for PVC cement to fill in. PVC cement is actually a solvent that “melts” the surface of the pipe, allowing it to bond to the fitting. You may have a really hard time dry fitting the components together. It is possible they can get locked together by friction and will be difficult to pull apart. So, keep in mind that some fittings can be dry fitted, some can’t. That’s why accurate measurements are important when planning the system’s dimensions and cutting PVC pipe.

Using Primer and PVC Cement

PVC cement is not really like cement or glue. It is a special solvent designed to slightly dissolve the PVC surface of pipe and fittings. Once the PVC components are assembled, the solvent evaporates and the PVC re-hardens. The two components are now one. They’re “welded” together with a water-tight seal. To get a water-tight seal the pipe end must be square, free of burrs and free of dirt and oils. It’s the same with fittings. To assemble your system, you’ll need PVC primer and PVC cement. There are several kinds of cements (and primers) available, each formulated for specific types of plastic. Make sure the products are specifically for PVC. CPVC pipe cement is made for CPVC (chlorinated polyvinyl chloride) pipe, and should not be used with PVC.

Why use PVC Primer?

PVC primer starts a chemical reaction that softens the PVC and washes away residue from the plastic surface. Primer reduces the chances of poor bonding between the PVC parts. Primer is typically dyed purple. This makes it easy for plumbing inspectors to see if primer was used on a home’s plumbing system. Some aquarists don’t like the look of purple stains on their filtration system. PVC can be cemented without primer but you must be sure there is no grease or oils on the components when you glue them together.

How to Cement PVC

The following steps include using primer when assembling your PVC system. Have all your components ready before starting the assembly process. You’ll want to work relatively fast when working with primer and cement.

infographic of steps 1 - 3 on how to glue pvc parts

  1. Using the dauber on the can’s lid, apply primer to the fitting and PVC pipe. Primer is only active while it is wet, which is about 10 seconds.
  2. Immediately apply PVC cement to the same areas that are primed. Typically, that’s the end of the pipe and inside the fitting.
  3. Twist the pipe a quarter turn as you push it into the fitting. This will cause the cement to spread and fill any gaps. The softened PVC will allow you to completely push the pipe into the fitting.
  4. *Hold the pipe and fitting together firmly for about 30 seconds. If not supported when first assembled, some loose connections could rotate or pull apart.
  5. Check for alignment. You have a very short amount of time to make slight corrections.
  6. Wipe away excess cement, for a cleaner look.
  7. Allow the cement to cure for 24 hours before pumping water through the system.

Primer and PVC cement can get messy when you assemble plumbing. Prepare for drips by placing cardboard under your work. Gloves will protect your hands from the solvent and purple primer stains.

Pro Tip: Working with Threaded PVC Fittings

PVC and plastic fittings use tapered threads. All tapered pipe threads have a small spiral leak path between the mating threads.  The leak path needs to be sealed during the assembly process to obtain a leak free connection. The most common solution is the use of Teflon tape.

diagram of threaded pvc and where it tends to leak from

Teflon tape is wrapped around the male threads to assemble the PVC. The idea is to plug the leak path with the layer of tape. While Teflon has been used with success, pros don’t recommend it. Here’s why. The slippery Teflon makes it easy to over-tighten the fitting. This can cause the female fitting to develop stress cracks and leak. The Teflon tape also “bunches up” in the threads, putting more pressure on the female fitting. If the male fitting is backed out a little, the Teflon seal is often lost, allowing for drips. While many aquarists have used Teflon tape with success, pros recommend a non-hardening sealing paste. After applying the paste, hand-tighten the fitting until snug then tighten one to two more turns at most. This is all that’s required for a stress-free connection that won’t leak. Avoid using a wrench if possible.

Final Thoughts

Working with PVC is not difficult once you know the process. Most of the work is in the planning stage. A good approach is to check out what others have built and then adapting their ideas to your aquarium. If you happen assemble the PVC and make a mistake or want to change something, you can. You don’t have to scrap the project. Union couplers allow you to cut a pipe, make modifications and reassemble the system. There are countless fittings and accessories for creating your own system. If you can dream it, you can build it.

Check out the rest of this 4-part series at the following links: