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A bulkhead fitting is installed through a hole in the wall of a tank, barrel, or container. The fitting passes through the hole, and a gasket is compressed against the tank wall to make a watertight seal.
The basic process is simple: drill the correct-size hole, clean the surface, insert the bulkhead fitting, position the gasket correctly, and tighten the retaining nut without overtightening it.
What Is a Bulkhead Fitting?
A bulkhead fitting is a plumbing fitting that creates a sealed connection through the wall of a container.
It is commonly used on:
- Rain barrels
- IBC totes
- Water storage tanks
- Cisterns
- Aquaponic tanks
- Irrigation reservoirs
The fitting usually has four main parts:
- A threaded fitting body
- A sealing gasket
- A retaining nut
- Internal or external pipe threads for connecting plumbing
Once installed, you can attach a valve, hose adapter, pipe, pump line, overflow pipe, or other plumbing component.
Where Does the Gasket Go?
For most bulkhead fittings, the gasket goes against the flange side of the fitting.
The flange is the wide, flat part of the bulkhead body. It usually sits on the side where the seal is intended to form.
For a typical rain barrel installation:
Inside the tank:
Flange → gasket → tank wall
Outside the tank:
Tank wall → retaining nut
However, bulkhead fittings are made in several designs. Some manufacturers specify a different gasket arrangement.
Follow the fitting manufacturer's instructions if they differ from this general setup.
Do not automatically add gaskets to both sides unless the fitting is designed that way. An extra gasket can sometimes allow the fitting to shift instead of improving the seal.
How to Install a Bulkhead Fitting
1. Choose the Installation Location
Pick a flat, smooth section of the container wall.
Avoid installing the fitting:
- Across a molded seam
- On a sharp curve
- Over raised lettering
- Near damaged plastic
- Where the tank wall changes thickness
- So close to the bottom that you cannot tighten the nut
A flat surface gives the gasket the best chance of sealing evenly.
For a rain barrel outlet, the fitting is normally placed near the bottom while leaving enough clearance for the valve and any plumbing attached to it.
2. Check the Required Hole Size
Do not choose the drill size based only on the nominal pipe size.
For example, a bulkhead sold as a 1-inch fitting normally needs a hole considerably larger than 1 inch because the entire threaded body must pass through the tank wall.
Use the hole diameter specified for your exact bulkhead fitting.
This is one of the most important parts of the installation.
A hole that is too small can damage the fitting or tank when you force it through. A hole that is too large may prevent the gasket from sealing properly.
3. Mark the Hole
Mark the center of the opening.
Before drilling, check both sides of the tank if possible. Make sure the fitting will not interfere with:
- Tank ribs
- Internal supports
- Existing outlets
- Valves
- Pumps
- Downspout connections
Also confirm that you can reach the retaining nut.
Some tanks have openings large enough to reach inside. Others require fittings designed for installations where inside access is limited.
4. Drill the Hole
A hole saw is commonly used for plastic barrels and tanks.
Keep the drill square to the tank wall so the opening is reasonably straight.
Use care with thin plastic. Pushing hard can cause the material to crack, tear, or deform.
Large tanks should be empty before drilling unless their manufacturer specifically permits otherwise. Water adds a great deal of weight and pressure against the tank wall.
5. Remove Burrs
Clean the edge of the hole after drilling.
Remove:
- Plastic shavings
- Sharp edges
- Burrs
- Dirt
- Old sealant
The gasket should rest against a smooth surface.
You usually do not need to aggressively sand the tank. The goal is simply to remove material that could prevent the gasket from sitting flat.
6. Clean the Sealing Surface
Wipe the area around the hole clean.
Check the gasket as well. It should be clean, undamaged, and lying flat.
A piece of grit trapped under the gasket can create a small leak path.
7. Insert the Bulkhead Fitting
Place the gasket against the flange as required by the fitting design.
Push the fitting body through the hole.
For many rainwater tanks, the flange and gasket are installed on the inside of the tank, with the retaining nut outside.
Make sure the gasket stays centered and flat as the fitting is inserted.
8. Install the Retaining Nut
Thread the retaining nut onto the bulkhead body.
Start it by hand.
The nut should turn smoothly. If it immediately feels crooked or unusually tight, stop and restart it. Cross-threading can damage plastic threads.
Tighten the nut until the gasket is evenly compressed.
9. Do Not Overtighten It
More force does not necessarily create a better seal.
Overtightening a plastic bulkhead fitting can:
- Distort the gasket
- Crack the fitting
- Strip the threads
- Deform a thin tank wall
- Create a leak instead of stopping one
Hand tightening is often enough for small plastic fittings, sometimes followed by a modest additional turn if the manufacturer specifies it.
Use the fitting manufacturer's tightening instructions when available.
Do You Need Sealant on a Bulkhead Fitting?
Usually, the gasket creates the seal between the bulkhead and the tank.
Plumber's tape, pipe dope, or silicone should not normally be used as a substitute for a properly installed gasket.
Adding sealant between the gasket and tank can sometimes make the gasket slide or squeeze out while the nut is tightened.
Sealant may be appropriate for threaded plumbing connected to the bulkhead, depending on the thread type and manufacturer's instructions.
That is separate from sealing the bulkhead against the tank wall.
If a new bulkhead fitting leaks, first check the hole size, gasket position, installation surface, and tightening before covering the connection with sealant.
How Tight Should a Bulkhead Fitting Be?
Explore practical steps for fiting a bulkhead to understand likely upkeep demands over the system’s service life.
It should be tight enough that the gasket is compressed evenly and the fitting cannot move easily.
It should not be tightened until the gasket bulges dramatically or the tank wall bends.
Plastic fittings need particular care because excessive wrench force can damage them.
If the manufacturer provides a torque specification, use it. Otherwise, tighten gradually and leak-test the connection before applying more force.
How to Leak-Test the Installation
Do not immediately fill a large storage tank completely.
Add enough water to cover the bulkhead fitting first.
Then inspect:
- Around the gasket
- Around the fitting body
- Below the retaining nut
- Around connected valves or pipe threads
Dry the area with a cloth and check again. Very slow leaks can be hard to see on an already wet tank.
If the fitting is dry, raise the water level gradually.
Water pressure increases as the water above the fitting gets deeper, so a connection that stays dry under a few inches of water should still be checked as the tank fills.
What If the Bulkhead Fitting Leaks?
Do not immediately tighten it as hard as possible.
Drain the water level below the fitting and inspect the installation.
Common causes include:
The gasket is on the wrong side
Check the fitting instructions and reposition it correctly.
The gasket is twisted
A folded or pinched gasket cannot seal evenly.
Remove the fitting and reinstall it with the gasket lying flat.
The hole is rough
A burr or piece of debris may be creating a leak path.
Remove the fitting and smooth the sealing surface.
The hole is too large
The gasket needs enough tank wall around the opening to create a seal.
A badly oversized hole may require repair, a larger fitting, or another suitable solution rather than additional tightening.
The fitting is overtightened
Excessive compression can distort the gasket or tank wall.
Loosen the fitting, inspect the gasket, and reinstall it correctly.
The tank surface is curved or uneven
Bulkhead fittings seal best on flat surfaces. A heavily curved wall may prevent uniform gasket compression.
Installing a Bulkhead Fitting in a Rain Barrel
Rain barrels are usually one of the easier bulkhead installations because the plastic walls are relatively thin.
Before drilling, plan what will connect to the fitting.
For example, an outlet might need room for:
- A ball valve
- Hose adapter
- Garden hose
- Irrigation line
- Short pipe nipple
Do not put the hole so low that the valve hits the ground or barrel stand.
Leaving the outlet slightly above the absolute bottom can also allow small amounts of sediment to settle below the withdrawal point.
Installing One in an IBC Tote
IBC totes need a little more planning.
Their plastic inner containers are surrounded by a metal cage, so the fitting location must clear the cage structure.
Check that:
- The fitting can pass through the tank wall
- The nut can be tightened
- The external plumbing clears the cage
- The fitting does not weaken an unsuitable part of the container
If the tote already has a usable factory outlet, using that outlet is often simpler than cutting another large opening.
Also consider what the tote previously contained. A used IBC tote should not automatically be considered suitable for water intended for drinking or household use.
Should the Flange Be Inside or Outside the Tank?
Either arrangement can work if the particular fitting is designed for it, but many installations place the flange and gasket inside the tank.
One reason is water pressure. The water pushes the flange toward the tank wall rather than away from it.
Installation access may determine the orientation on some systems.
The key rule is to keep the gasket against the sealing face specified by the fitting manufacturer.
Can a Bulkhead Fitting Be Installed on a Curved Barrel?
Sometimes, but a flatter location is preferable.
A flexible gasket can accommodate a small amount of curvature. Heavy curvature can prevent the flange and gasket from pressing evenly against the wall.
The larger the fitting, the more noticeable this problem can become because the flange spans a wider section of the curved surface.
Avoid forcing a rigid fitting flat by heavily tightening the nut. That can deform or crack the barrel.
Plan the Plumbing Before Cutting the Hole
The hardest mistake to correct is a hole drilled in the wrong place.
Before drilling, temporarily hold the fitting, valve, and connected pipe near the proposed location.
Check:
- Clearance around the fitting
- Space for a wrench or hand
- Hose direction
- Pipe support
- Tank stand clearance
- Overflow or drain locations
- Pump suction requirements, if applicable
Connected plumbing should also be supported when necessary. A heavy valve or long section of pipe can put leverage on the tank wall and bulkhead fitting.
Frequently Asked Questions
Which side does the gasket go on a bulkhead fitting?
On most bulkhead fittings, the gasket sits against the flange side of the fitting and directly against the tank wall. Follow the manufacturer's instructions because some designs differ.
Do bulkhead fittings need silicone?
Usually not. The gasket normally creates the tank seal. Silicone should not be used to compensate for an incorrect hole, damaged gasket, or poorly installed fitting unless the manufacturer specifically calls for it.
Can I install a bulkhead fitting without reaching inside the tank?
Some fittings and installation methods are made for containers with limited inside access. A standard bulkhead fitting normally requires access to both sides so the fitting body and retaining nut can be assembled correctly.
How big should the hole be for a bulkhead fitting?
Use the hole diameter specified for the exact fitting. Do not assume the hole should match the nominal plumbing size because the bulkhead body is larger than its pipe connection.
How do I stop a bulkhead fitting from leaking?
Drain below the fitting and inspect the gasket position, hole size, sealing surface, threads, and tightness. Reinstalling the fitting correctly is usually better than simply adding more sealant or tightening it harder.
Can I put a bulkhead fitting near the bottom of a rain barrel?
Yes. Bottom outlets are common, but leave enough room for the fitting, valve, hose, and barrel support. Placing the outlet slightly above the very bottom can also leave space for settled debris.
Can you overtighten a bulkhead fitting?
Yes. Overtightening can distort the gasket, crack the fitting, damage the threads, or deform the tank wall. Tighten only enough to compress the gasket evenly and follow the manufacturer's instructions when available.
