PVC plumbing and bulkheads for an aquarium overflow

If you’ve got a reef or advanced freshwater aquarium, chances are there are some PVC components somewhere in the filtration system. PVC pipe, elbows, and other fittings are used in protein skimmers, filter sumps, refugiums, algae scrubbers, media reactors, and overflow boxes. Whether you’re building a filtration system from scratch or modifying the system that came with your tank, it’s important to understand the basics of PVC plumbing and components.

The History of PVC

PVC is short for polyvinyl chloride. The compound was first discovered in 1872 by Eugen Baumann, a German chemist. No one really knew what to do with the new substance until a researcher at B.F. Goodrich modified the formula to create a synthetic rubber-like material. It was used for manufacturing heels for shoes and golf balls.

New processes were developed to create a more ridged form we know as PVC pipe. But did you know PVC is found in credit cards, wiring, floor tiles, and more. PVC is the third most used plastic today. It is commonly used in liquid handling applications like household plumbing, irrigation systems, and aquarium filtration. PVC components are relatively strong, resistant to harsh environments, like saltwater, and inexpensive.  PVC is easy to cut and fabricate into intricate plumbing projects. That’s why it is used so much to build or modify aquarium filtration systems.

PVC Pipe Schedule Ratings

PVC Schedule diagram

PVC pipe has something called a schedule (SCH) rating. The concept of schedule ratings started with steel pipes. When PVC pipe came along the idea of SCH ratings was applied to the new plastic pipe. The most common types of PVC pipe are SCH 40 and SCH 80. A PVC pipe’s schedule has to do with the thickness of its walls. Schedule 80 PVC has thicker walls than SCH 40 pipe. The larger the schedule rating the stronger the pipe. Schedule 40 PVC is white in color, while schedule 80 is usually gray. Make sure you look for the SCH rating printed on the pipe to be sure.

Most aquarium applications can use either schedule 40 or schedule 80.  It is not uncommon to use Schedule 80 fittings with schedule 40 PVC pipe.

Understanding PVC Sizing


pvc pipe dimensions referring to the Inner Diameter (ID) vs the Outer Diameter (OD) for plumbing

The outside diameter is not the PVC pipe size! PVC pipe sizes are identified by the inside diameter (ID) of the pipe. Don’t make the mistake of measuring the outside diameter of your PVC pipe. That will give you a larger and incorrect size. The pipe (outside diameter) will always be larger than the size name. This is because of the thickness of the wall. For most projects you’ll be using ½”, ¾” and 1” PVC plumbing.

infographic of standard ID and OD sizes

Matching Your PVC Pipe and Fittings

Matching PVC pipes and fittings is easy. Once you know the size pipe you’re working with, just match it to the corresponding fitting size. A 1/2" fitting will fit on a 1/2" pipe. This is true for both schedule 40 and 80 PVC components.

PVC Fitting Types and Terminology

There are many kinds of fittings made for PVC pipe. They make it easy to design and connect any kind of aquarium gear to your tank. Here’s a list of common fittings and an explanation of what they’re used for.

  • Slip Fitting:  A fitting with no threads that slips over the pipe. It requires primer and glue (solvent and cement) to create a leak-proof seal.
  • FPT or FIPT: A female pipe threaded connection. The threads are on the inside of the fitting. It screws onto a male pipe thread fitting.
  • MPT or MIPT: A male pipe threaded connection with threads on the outside of the fitting. It connects to a female pipe threaded connection.
  • Coupling or Union: A simple straight fitting used to join two parts together. The union coupler has threaded tightening collars on one or both ends for easy installation or removal of the connected parts. They’re often used on PVC plumbing sections that may require removal in the future. Couplers can be slip or female threads or a combination of the two. You can join pipe to pipe, pipe to fitting or fitting to fitting.
  • Tee and WYE: A “T” shaped fitting to connect parts in three different directions with two being a straight line and one creating an angle (usually 90 degrees). Tee fittings can have a slip or threaded connections.
  • Pipe Nipple: This adapter is a simple threaded section of PVC. It’s used to join two female threaded adapters.
  • Elbow:  An angled fitting used to make a turn in the PVC line. Elbows are available in 90- and 45-degree angles. Elbows come in slip or threaded connections.
  • Adapter: There are many types of adapters. They’re used to adapt from one type of part to another. The most common applications are slip to a threaded connection.
  • Bushing: Its similar to an adapter, but is mainly used to join pipes of two different sizes together.
  • End Cap: An end cap is a fitting that seals the end of your pipe. This fitting normally has a slip fitting that attaches to the pipe with glue.
  • Plug: It has the same purpose as the cap but it has a threaded plug that screws onto the fitting. The plug can be removed to drain the water from the pipes.

CPVC and Why you Don’t Need It

You may have seen tan-colored plastic pipes and fittings in a local home improvement store which is called CPVC or chlorinated polyvinyl chloride. It’s an industrial-style plastic plumbing designed to withstand hot and corrosive liquids. There is no benefit to using CPVC pipes or fittings on your aquarium.

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