Common Plumbing Terms

  • FPT - Female pipe thread
  • MPT - Male pipe thread
  • Slip - Smooth surface for gluing PVC pipe
  • Thread - Threaded fitting
  • Spigot - male side of a slip fitting
  • Hose Barb / Insert Fitting - Barbed fitting designed to make a watertight connection with flexible vinyl tubing
  • PVC Pipe - Polyvinyl chloride, a rigid plastic piping used for many plumbing applications
  • Flexible PVC - Plastic pipe similar to PVC with the added benefit of flexibility
  • Flexible Tubing - Flexible tubing
  • Teflon Tape - Tape made out of Teflon used for wrapping around threaded plumbing connections to ensure a watertight seal
  • I.D. - Inner diameter
  • O.D. - Outer diameter
  • U-Tube -  A U-shaped rigid pipe used to secure vinyl tubing to your aquarium
  • Flow Accelerator - A special type of nozzle used to increase water flow
  • Impeller - A wheel of blades—usually attached to a magnet—inside a water pump used to move water through the pump as it spins

Aquarium Plumbing Guide


bulkhead Threaded Bulkhead

Bulkhead fittings allow you to make a sealed connection into a container such as an aquarium or sump. The fittings are designed to be installed through your container and sealed with a rubber gasket and nut via a hole drilled through the container.

Each side has either a standard threaded connection for use with threaded plumbing parts or slip connections for gluing PVC pipe and fittings into the bulkhead. You will always attach your PVC or fittings to the inside of the bulkhead. The threads on the outside of a bulkhead are for use only with the sealing nut mentioned above when you first install the bulkhead.

bulkhead Slip Bulkhead

Bulkheads are measured based on the inside connections. Therefore, a 1" double-threaded bulkhead fitting will work with 1" standard threaded plumbing parts. You will also notice a "hole size" which is the required diameter of the hole you need to fit the bulkhead through the wall of your container. This hole size is very important when choosing bulkheads in order to fit a pre-drilled sump or aquarium.

Bulkheads are most commonly used for attaching external pumps to your sump and installing drain or return lines into a drilled aquarium or container.

Barbed or Insert Fittings

Plumbing Hose Barb Fitting

A hose barb fitting is designed to make a water-tight connection with flexible vinyl tubing from a pump, pipe, or bulkhead. The fittings will be barbed to help keep them sealed inside the vinyl tubing.

The insert fittings come with threads or slip fittings for easy connection with bulkheads, PVC pipe fittings, or pumps.

The sizes advertised correspond to the inner diameter of the tubing that fits the barbed end along with the standard pipe size of the thread or slips connection. For example, a ¾" MPT x ¾" Insert has ¾" male pipe threads for connection on one side and works with ¾" inner diameter flexible tubing on the other. It’s important to utilize the correct size hose barb to ensure all your tubing connections are watertight and free of leaks.

Hose clamps

Plumbing Hose Clamps

Should be used on the outside of flexible tubing to secure the tubing onto a barbed fitting and ensure a water-tight seal. 


Plumbing Flexible Vinyl Tubing

The most commonly used tubing in the aquarium hobby is flexible vinyl tubing. Flexible vinyl tubing comes in either clear or black color and is easily plumbed using a hose barb mentioned above. Flexible vinyl tubing can kink if you are trying to make 90° corners, so be careful when plumbing in tight spaces. This tubing is best used for applications up to 1". The flexible vinyl tubing we carry has a thick wall to help prevents kinks. This type of tubing is measured based on the inside diameter. Be sure to match your pump connection size accordingly and always use a hose clamp to secure the connection.

Flexible PVC and Ultra Flex Pipe are flexible tubing made out of PVC plastic. They will work with most any slip-style PVC fittings and standard PVC cement. This style of tubing is available in sizes up to 2" and is measured based on the inside diameter. There are many benefits to using this type of flexible tubing. It allows you to create a clean, permanent plumbing system that reduces pressure on your pumps. It also allows you to form angles that would not be possible with rigid PVC pipe. This type of tubing is not compatible with hose barb fittings and will need to be glued in place using slip fittings.


Plumbing Overflow Strainer

Overflow strainers are designed for aquarium drains to prevent debris from entering or blocking the drain. They are available with either standard size slip or threaded connections and will attach directly into a bulkhead in most scenarios. 


Plumbing Loc-Line Ball Socket Flexible Tube

Loc-Line is a brand name flexible piping that utilizes ball and socket joints to accomplish permanent angles in your piping. This is generally only utilized inside the tank as a nozzle for the return water and can be angled to suit your rock-work or aquascape. It’s useful to help spread out your return flow and provide flow to multiple areas of your tank.

This type of piping is modular and can be expanded to suit most any situation. Loc-Line pliers, available in ½" and ¾" sizes, make it easy to assemble multiple parts. With the use of the male threaded connector, you can easily attach to any female threaded connection such as a bulkhead or return U-Tube.

Ball Valves and Gate Valves

Plumbing Ball Valve

Ball valves and gate valves are simply shut-off valves that allow you to block water from entering or flowing through your plumbing. They also can help to regulate the rate of water flow through your pipes or tubing.

Ball valves are nice when you need to shut off water flow to a particular area of your plumbing. The valves will quickly block the flow with a simple 90-degree turn of the handle. They are easily plumbed inline using threaded or slip connections.

Gate valves utilize a wheel that slowly closes a gate inside the valve giving you more precise control when attempting to control the flow of water. The valve requires multiple turns in order to close completely and is best used with rigid or flexible PVC.


Plumbing Union Fitting

A PVC union will provide you with a removable connection in your plumbing. These are very useful when plumbing aquariums as it allows you to disconnect and remove equipment or valves for maintenance. The valves can be glued or threaded into place and should be installed before and after all your valves and pumps. You can then easily unthread the union and remove your pump/valve with ease. Some valves and pumps even come with a union attached making maintenance easy.

Check Valve

Plumbing Swing Check Valve

Check valves are used as a one-way flow valve designed to allow water to flow only one direction through your plumbing. When your return pump is switched off, tank water can back siphon down your return plumbing and overflow your sump or water reservoir. These one-way check valves will prevent this from happening.

The valves we carry have no metal parts and should be cleaned regularly to ensure proper function. If not cleaned, the valves can fail and become unreliable. They utilize a single flap with rubber seal in order to block the water flow.

The valves are typically plumbed inline after your return pump. They come with standard slip or FPT connections and with or without unions. The union allows you to remove the valve for easy cleaning. They can be used in a number of other plumbing situations as well, but this is the most common use for aquariums.

Frequently Asked Questions 

What kind of PVC glue is safe for use with my aquarium?

Most standard PVC cement is safe. Just be sure to let it cure/dry completely before running water through the pipes. Using clear cement is best which makes for a clean installation, especially when using white PVC pipes.  Slips fittings require PVC cement whereas threaded fittings do not. 

My external pump is leaking. What should I do? 

First, check your pump connections to ensure they are tight, and use Teflon tape if needed. Then wipe the pump clean and attempt to locate the leak. Some pumps have replaceable seals and bearings which can wear out over time and leak. If it is your plumbing, you may need to shut down the pump and replace the necessary fittings to stop the leak. If you are using threaded fittings, hairline cracking is not uncommon because of the tapered threads so be careful not to overtighten.

My pump stopped moving water. What happened?

First, unplug the pump and disconnect it from your plumbing. Then remove the impeller cover and inspect the impeller for any cracks or damage. Also, inspect the impeller housing for any debris or damage. Clean both the impeller cover and impeller thoroughly to remove any build-up. Even the slightest layer of calcium or build-up covering the impeller area can stop the pump. 

Proceed to reseat your impeller, assemble the pump and test it in a bucket of water. Following this cleaning sequence solves the majority of pump problems if there are no obvious signs of damage found. If the impeller is damaged, source a replacement. 

It is possible for a pump motor to burn out too which means the impeller won't spin, and it won't pump water. If this is the case, you will need to replace the pump.  

What size bulkhead do I need?

We have just the article for you. Read: How To Select and Install Bulkheads

Should I use a check-valve?

This is often debated because check valves are never 100% effective.  They can and will fail eventually.  The best approach is to ensure your sump can hold 100% of the water that will back-siphon from your aquarium during a power outage.  That being said, many hobbyists still install a check valve to be safe.  Clean your check valve regularly to avoid build-up which causes failures. 

Should I use PVC or Flexible Tubing?

Again, this is a personal preference. PVC often looks more polished and you get the option of colors which adds a nice personalization touch to your filtration. PVC is also more permanent meaning once you glue it, it is difficult to changes things around.  Being rigid, PVC also is susceptible to vibration which can increase operating noise. 

Flexible tubing is easier to work with, easy to change and replace, and absorbs vibrations.  That said, it's not easy to use for advanced plumbing applications and does not look as nice. 

Do I need a union?

If using PVC pipe, unions are your friend. They make it easy to disconnect pipes and equipment for cleaning and to change things up if need be. You most certainly want a union attached to your return pump for easy disconnect and it's not a bad idea to have one on each of the drain lines as well. This way you can disconnect all of the plumbing from your tank without having to mess with any bulkheads. 

Can I reduce the diameter of the pipe?

It is best to carry the pipe diameter of your bulkheads to and from your tank but you can make reductions if necessary.  Reducing the pipe diameter slows down the flow so you want to avoid it in most cases. 

Schedule 40 or Schedule 80 PVC, which is best? 

Schedule 80 is simply a thicker PVC material that can handle higher-pressure applications. Some might say it also looks nicer and is most certainly more expensive. We often recommend Schedule 80 PVC fittings which are compatible with standard schedule 40 PVC pipe. 

Why use colored PVC? 

This is purely aesthetic and colored PVC serves no additional function over plain white PVC outside of looking way better. You could technically color code your drain lines and return lines to make differentiating them easier, but most of it is just aesthetic. 

How big should my sump be?

Generally speaking, your sump should be no less than 25% of your tank's total water volume. For example, a 100-gallon tank should have a minimum sump size of 25 gallons. Most hobbyists will tell you to get the largest sump that will fit your available space and budget. 

Do I need to use hose clamps?

All flexible tubing connections should be secured with a hose clamp.  If it is underwater, be sure to use a plastic hose clamp because the metal ones may rust.