Plumbing 101

I have read many DIY plans over the years and have also written a few myself. One of the things I have noticed is many articles make the assumption that you know all of the terms and methods needed to build the project. I have answered many of these types of questions in the DIY forum here at Reef Central in a piecemeal form. Hopefully, by putting this information in one place for easy reference, it will help you with all of your future DIY projects.

In the coming months, this column will cover more general construction methods, as well as specific DIY projects. I hope that this column will allow you to build things that you would not have attempted to in the past, as well as improve your results. DIY projects don't always save you money, but they are always a learning experience and a lot of fun. You will also have a sense of pride knowing you built it yourself.

Plumbing Terms

Here is a list of cryptic plumbing acronyms that you will run into from time to time and what they mean. Now, when you go into the plumbing store you will be able to talk like a real plumber.

OD Outside Diameter
ID Inside Diameter


NPT National Pipe Taper pipe threads are tapered unlike normal bolts and nuts, which are straight. Most pipe threads you will run into will be tapered.
NPS National Pipe Straight
FNPT Female National Pipe Taper, a fitting with internal threads.
MNPT Male National Pipe Taper, a fitting with external threads.
TPI Number of threads per inch.
GHT Garden Hose Thread. GHT is not NPS. It is it's own diameter and TPI.
Slip A PVC fitting without any threads that is intended to be glued.
Street A fitting that on one side has the same OD as a piece of pipe that size. This allows it to slip or screw if it has threads into another fitting like a piece of pipe. Sometimes called a Spigot fitting.
Reamer A pipe reamer is tapered like a NPT tap so the tapered tap has a tapered hole to thread. The taper rate is 3/4" per foot.

NPT Reamer
NPT tap

Pipe Tap to Drill Size Table

If you need to drill a hole for a threaded fitting in your project this table will tell you what size drill bit you will need to use. There are several ways to drill holes in PVC and acrylic. One way is to buy drill bits that were designed to drill plastic. They are available in a few sizes. US Plastic Corp. carries them. The next way is to make your own by using Bob's instructions at my Website on how to grind a normal speed bit so it will drill plastic. UniBits work very well also, the best price I have found for them is at Enco. A normal hole saw also works if you can find one the right size.

Pipe Tap Size - TPI
Drill Bit Without Reamer
Drill Bit With Reamer
1/16" - 27
1/8" - 27

1/4" - 18

3/8" - 18

1/2" - 14

3/4" - 14

1" - 11 1/2

1 1/4"  - 11 1/2

1 1/2" - 11 1/2

1 3/4" - 11 1/2

2" - 11 1/2

2 1/2" - 8

3" - 8

3 1/2"




C (.242)
Q (.332)

1 9/64"

1 31/64"

1 23/32"


2 3/16"

2 39/64"
3 15/64"

A (.234)


1 1/8"

1 15/32"

1 45/64"

1 15/16"

2 11/64"

2 25/32"
3 9/32"
3 3/4"
4 1/4"
5 1/4"
6 1/4"


PVC Pipe Sizes

PVC pipes are sized by their ID (inside diameter) but sometimes, in DIY projects, we also need to know their OD (outside diameter). Having this information will help us size other things to PVC fittings like acrylic tubing.

Schedule 40
Schedule 80
1 1/4"
1 1/4"
1 1/2"
1 1/2"
2 1/2"
2 1/2"

Solvent Cement Joining of Plastic Pipe FAQ

Here are some answers to questions about solvent cementing pipes. The better we understand these processes, the better job we will be able to do to make leak proof joints.

How does solvent cement work?
The solvents penetrate the plastic surface and cause the plastic to swell. The swelling continues until the gaps between the pipe and the fitting walls are closed and pressing against each other.

What plastics can be solvent cemented?
PVC (Polyvinyl chloride) , CPVC (chlorinated polyvinyl), ABS (Acetylonitrile-Butadiene-Styrene), polycarbonate [PC or Lexan] Styrene, Geloy and other plastic materials.

What plastics can not be solvent cemented?
Polyethylene, polypropylene, polybutylene, nylon and other engineering plastics (usually polyolefins).

What about using solvent cement when a joint is wet?
All solvent cements have the ability to absorb some water and still perform well enough to effect an adequate joint. However, research shows that the presence of 10% water in solvent cement can slow penetration and swelling by 65%. This joint with water inside will always be an inferior joint and subject to problems.

What is the difference between pipe cleaner and pipe primer?
A pipe cleaner is a mixture of solvents used to clean any dirt or foreign materials on the surface of the pipe which could prevent the penetration of the cement into the pipe surface. The cleaner must be wiped off with a clean rag immediately. A primer is a mixture of solvents used to penetrate the pipe and fitting and start the swelling process ahead of the application of the solvent cement. It is not wiped off. The solvent cement is applied on top of the primer immediately while wet.

What is the difference between set and cure time?
Set time is that initial period of swelling required to give the joint enough strength to be gently handled. Cure time is the total time period of required swelling for the joint to acquire enough strength that it can perform it's job transporting materials through it (at whatever pressure and temperature required) without coming apart or leaking.

What makes a good solvent cement joint?
A) User selects the proper cement and follows proper procedures
B) Cut pipe square
C) De-burr pipe inside and out
D) Check the dry fit
E) Use pipe cleaner when necessary
F) Use pipe primer on every joint
G) Apply cement properly
H) Insert pipe into the fitting properly
I) Wait for the proper set and cure times

Solvent Cementing Instructions

This is the five step process for making a good solvent cement pipe joint. We often have questions about how long a joint needs to set before we can use it. This explains that temperature, humidity and pipe size all effect setup and cure time. Using a joint before it is fully cured, will allow moisture into the joint which will weaken it which may lead to future failure.

1. Condition the pipe and fittings so that they are at the same ambient temperature. Cut the end of the pipe square by using a fine-toothed hand saw and miter box or power saw. Tube cutters with wheels designed for use with PVC are acceptable, provided they do not leave a raised bead on the outside diameter of the pipe. There are shears available for cutting small diameter PVC pipe also.

Note - Cutting PVC Pipe
You can cut PVC pipe with almost anything. They make handsaws especially for cutting PVC. You can use a circular saw with a plastic cutting or plywood blade. They also make shears for cutting PVC up to 1" and they work very well. The important thing is to have a straight and square cut on the end of the pipe so it seats all the way to the bottom of the fitting all of the way around.

PVC Pipe Cutter
PVC Shears

2. Using a chamfering tool or file put a 10 to 15 degree chamfer (bevel) on the end of the pipe.

Note - Beveling PVC Pipe
Before you glue a fitting on a piece of PVC pipe you should bevel the PVC pipe. There are tools that do this. The ones for small PVC pipe (Figures 1 & 2) are very inexpensive but the ones for large PVC pipe (Figure 3) are over $100. These tools will round the inside edge of the pipe and will bevel the outside edge to 15 degrees. You can get the ones for small pipes at Home Depot, Lowes... and the large one from plumbing supply companies.

PVC Pipe Bevel - Figure 1
PVC Pipe Bevel - Figure 2
PVC Pipe Bevel - Figure 3

3. Check the dry fit of the pipe and fitting. Pipe should enter the fitting about 1/3 to 3/4 depth. Position the pipe and fitting to assure alignment. Using a clean rag, wipe the pipe surface and fitting socket to remove all dirt, moisture, and grease. If wiping fails to clean the surface, a chemical cleaner must be used.

4. Using a clean natural bristle brush about 1/2 the size of the pipe diameter, freely apply the primer to the fitting socket with a scrubbing motion until the surface is penetrated. Repeated applications may be necessary. Now apply the primer to the pipe surface equal to the depth of the fitting socket in the same manner, making sure the surface is well penetrated. Again apply primer to the socket, to make sure it is still damp.

5. Using a clean natural bristle brush (not a dauber brush) 1/2 the size of the pipe diameter, flow on a heavy coat of solvent cement to the male end of the pipe. Load the brush and do not trim. The amount should be more than sufficient to fill any gap. Next apply a liberal coat of solvent cement to the inside of the socket, using straight outward strokes to keep excess cement out of the socket. While BOTH SURFACES are STILL WET with solvent cement, insert the pipe into the socket with a 1/4 turn twisting motion. A pair of strap wrenches (shown below) or a vice and strap wrench will help with the 1/4 turn on pipes larger than you can turn by hand. The pipe MUST go to the BOTTOM of the socket. The application of solvent cement to pipe and fitting, and the insertion of the pipe into the fitting, should be completed in LESS THAN ONE MINUTE. If necessary, use two people to simultaneously apply the solvent to pipe and fitting. Hold the joint together for approximately 30 seconds until both surfaces are firmly gripped. Allow proper set time before disturbing joints. After assembly, a properly made joint will usually show a bead of cement around its entire perimeter, this should be brushed off. Allow the joint to cure for an adequate time before pressure testing.

Strap Wrench

Initial Joint Set Times

Temperature Range During Assembly

Pipe Sizes
Pipe Sizes
Pipe Sizes
  1/2" to 1 14/" 1 12/" to 3" 4" to 8"
60 to 100 degrees Fahrenheit
15 Minutes 30 Minutes 1 Hour
40 to 60 degrees Fahrenheit
1 Hour 2 Hours 4 Hours


Joint Cure Times at a Relative Humidity of 60% or Less

Temperature Range During Assembly Pipe Sizes Pipe Sizes Pipe Sizes
  1/2" to 1 14/" 1 12/" to 3" 4" to 8"
60 to 100 degrees Fahrenheit
1 Hour 2 Hours 6 Hours
40 to 60 degrees Fahrenheit
2 Hours 4 Hours 12 Hours

Working with Bulkhead Fittings
The main thing to remember about working with bulkhead fittings is to have the fitting you are going to use in your hand before you drill the hole for it. The reason for this is because there are a number of bulkhead fittings with the same ID that have a broad range of OD, which will require a different size hole. The brand and strength of the fitting will effect its OD. The gasket will always go on the head end of the bulkhead fitting never the nut end regardless which end of the fitting is in the water. A sealed fitting is a sealed fitting. Bulkhead strainers are nice for keeping creatures in your system from getting sucked down the drain and clogging it up.

Bulkhead Fitting
Bulkhead Strainer

Ball and Gate Valves
Ball valves and gate valves come in slip joint and FNPT with a union on one end or both. This makes it easy for you to be able to get exactly what you need for your project. Ball valves are best used for on/off applications. A gate valve works best if you need to adjust the flow between on and off.

Single Union Ball Valve
Dual Union Ball Valve


Gate Valve

A union allows you to have a connection in a pipe that can be opened up for service and then closed back up for a water tight seal. For a DIY project they also make a nice o-ring flange ready to glue onto your PVC or acrylic pipe.


Compression Fitting
A compression fitting allows you to adjust the length or rotation of two pieces of pipe.

Compression Coupling

Flexible PVC
Flexible PVC has the same ID and OD as rigid PVC pipe and you can glue regular PVC schedule 40 fittings on it. Use WELD-ON 725 Wet 'R Dry to glue it. Flexible PVC makes a very nice looking job and is very easy to work with.

Flexible PVC

No Tap, Through-wall Fitting
If you need to put a fitting through the wall of a PVC pipe you can make your own bulkhead fitting really cheaply. Get a PVC male adapter and female adapter. Drill a hole in the pipe where you want your fitting to go the size of the OD of the threaded part of the male adapter. Put some Teflon tape on the male adapter threads and put it through the hole in the pipe and screw the female adapter onto it until they both pull up against the inner and outer wall of the pipe. Now run a bead of Marine Goop around the fitting where it meets the pipe to seal the joint. You now have a fitting through the wall of your pipe for less than $1.

Through Wall Fitting

Small Tubing Fittings
Small tubing used on RO/DI systems and things like calcium reactors use two major brands of fittings, Jaco and John Guest Super Speedfit. The Jaco fittings crimp the tube in the fitting and the John Guest fittings are push in fittings. All you have to do to remove the tube from a John Guest fitting is depress a little ring around the tube and pull the tube out. There is a wide variety if each type of fitting. US Plastic carries most of them along with the colored tubing used with them. They come in 5/16" through 1/2."

Small Tubing Fittings

Where to Find Things
If you don't have a well-stocked plumbing supply near where you live, there are several good ones on the Internet.
They have almost anything and very good prices. They have 1/8" and 1/4" FNPT by 1/2" and 3/4" slip bushings which can be very useful in your project.

Savko Plastic Pipe & Fittings, Inc.
They also have a very nice selection of plumbing parts. If you don't see what you want, it is worth an email or a call because they have many things that are not on their web site.

Aquatic Eco-Systems Inc.
They have PVC shears, NPT taps and drill bits. They also carry a wide selection of bulkhead fittings and flexible PVC by the foot or the coil and the glue for it also.

United States Plastic Corp.
They have a nice selection of small threaded fittings and tools.

ALSCO Industrial Products, Inc.
They have a nice selection of tools for good prices and bulk PVC fittings.

For more information on plumbing and DIY information visit my homepage at Snailman's Reef.

I also invite you to read and share other DIY ideas at the DIY forum I moderate.

If you have any questions about this article, please visit my author forum on Reef Central.

Reefkeeping Magazine™ Reef Central, LLC-Copyright © 2008

Plumbing 101 by Jon Garner -