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A bulkhead fitting gives you a strong, threaded connection through the wall of a rain barrel. It can be used for a spigot, drain, overflow pipe, hose adapter, or connection between barrels.
The key is making a clean hole that matches the fitting, placing the gasket correctly, and tightening the fitting without crushing the barrel wall. Most leaks happen because the hole is too large, the gasket is on the wrong side, or the fitting is overtightened.
What Is a Bulkhead Fitting?
A bulkhead fitting is a connector made to pass through the wall of a tank or barrel.
Most bulkhead fittings have four main parts:
- A threaded fitting body
- A flange, which is the wide flat part
- A rubber gasket
- A large retaining nut
Once installed, the barrel wall is held between the flange and the retaining nut.
The fitting then gives you a threaded opening where you can connect a valve, pipe, hose adapter, or other plumbing part.
Before You Drill the Rain Barrel
Do not start by choosing a drill bit that looks close enough. Check the fitting first.
The pipe size printed on a bulkhead fitting is usually not the same as the hole size needed to install it. For example, a fitting sold for a certain pipe size needs a larger hole because the body of the fitting has to pass through the barrel wall.
Use the hole diameter specified by the fitting manufacturer whenever it is available.
Also check these points before drilling.
Make Sure the Barrel Wall Is Suitable
A standard plastic rain barrel usually has a wall thin enough for a bulkhead fitting. Very thick tanks may require fittings with longer threads.
The surface should also be reasonably flat.
A strongly curved section can make it hard for the gasket and flange to sit evenly. On a round barrel, choose an area with the least severe curve you can find.
Check the Inside Clearance
The nut must fit on the inside or outside of the barrel, depending on how the fitting is installed.
Make sure there is enough room for:
- The retaining nut
- Your hand or wrench
- Any internal pipe or screen
- Nearby ribs or molded shapes in the barrel
A location may look perfect from the outside but be impossible to reach from inside.
Decide What the Fitting Will Do
Location depends on its purpose.
A drain or spigot normally goes near the bottom, but not so low that the fitting hits the barrel floor or support stand.
An overflow fitting normally goes near the top.
A fitting that connects two barrels should be placed at a height that works with the plumbing arrangement you plan to use.
Leave enough space around the hole for the entire flange and gasket to sit against the barrel wall.
Tools and Materials
For a typical installation, you may need:
- Bulkhead fitting
- Hole saw of the correct diameter
- Drill
- Marker
- Tape measure
- Deburring tool, utility knife, or fine sandpaper
- Adjustable wrench or suitable large wrench
- Clean cloth
The barrel should be empty before you drill it.
If the barrel previously contained anything other than water or food-safe material, do not assume it is suitable for storing rainwater for your intended use.
How to Install a Bulkhead Fitting in a Rain Barrel
1. Choose and Mark the Location
Place the fitting against the barrel where you want it installed.
Check that the flange will sit flat and will not overlap a ridge, seam, molded label, or sharply curved section.
Mark the center of the hole.
Measure again before drilling. Once the hole is cut, moving it means plugging the old opening or replacing the barrel.
2. Confirm the Required Hole Size
Measure the fitting body or check the manufacturer's installation instructions.
The hole needs to be large enough for the threaded body to pass through without forcing it.
It should not be so large that the gasket has little barrel surface left to seal against.
Do not size the hole from the nominal pipe size alone.
3. Drill the Hole
Keep the drill as square to the barrel wall as practical.
Start slowly so the center bit does not wander. Once the hole saw begins cutting, use steady pressure rather than forcing it through the plastic.
Plastic can catch a hole saw as the cut finishes. Good control helps prevent the barrel wall from cracking or the drill from twisting suddenly.
If possible, support the area from behind without putting your hand near the cutting tool.
4. Remove Burrs
After drilling, inspect both sides of the hole.
Remove:
- Plastic curls
- Raised edges
- Sharp burrs
- Loose pieces
The area where the gasket sits should be smooth.
Do not aggressively enlarge the opening while cleaning it. A slightly rough edge can be smoothed, but an oversized hole is much harder to fix.
5. Clean the Sealing Surface
Wipe away plastic dust and dirt.
The gasket needs direct contact with the barrel wall. Debris trapped underneath it can create a small path for water to leak through.
6. Position the Gasket Correctly
Follow the instructions supplied with your particular fitting.
For many bulkhead fittings, the gasket sits against the flange on the side of the tank where the flange is located. It does not automatically belong on the side that contains the water.
Do not assume that adding a second gasket will improve the seal. Some fittings are designed for one gasket only.
The important point is that the gasket stays flat against the sealing surface rather than being twisted or pinched.
7. Insert the Bulkhead Fitting
Push the threaded body through the hole.
Make sure the flange and gasket are sitting evenly against the barrel.
The fitting should pass through without requiring heavy force. If it will not fit, check the hole for burrs before enlarging it.
8. Install the Retaining Nut
Thread the large retaining nut onto the fitting from the opposite side of the barrel.
Start it by hand.
If the nut becomes difficult to turn almost immediately, stop and check the threads. A nut started at an angle can cross-thread and damage the fitting.
9. Tighten the Bulkhead
Hand-tighten the nut until the fitting is secure and the gasket is evenly compressed.
Some fittings require additional tightening according to their manufacturer's instructions.
More force does not always create a better seal.
Overtightening can:
- Distort the gasket
- Bend a thin barrel wall
- Crack the barrel
- Damage plastic threads
- Make the fitting leak
The goal is even gasket compression, not maximum tightness.
Should You Use Silicone or Thread Sealant?
A properly installed bulkhead fitting normally seals against the barrel with its gasket.
Smearing silicone around the gasket is not a good substitute for:
- The correct hole size
- A smooth sealing surface
- Proper gasket placement
- Correct tightening
Sealant may also make future removal more difficult.
Thread sealant is a separate issue. The bulkhead gasket seals the fitting to the barrel wall. Connections screwed into the threaded opening may need an appropriate thread-sealing method depending on the type of threads and the connected parts.
Study the origin and function of bulkhead fittings to assess the compromises that affect the upcoming system choice.
Do not use thread tape or sealant to compensate for incompatible threads.
Connecting a Spigot to the Bulkhead Fitting
Once the bulkhead is secure, you can install a compatible spigot or valve.
Check:
- Thread type
- Thread size
- Whether the connection is male or female
- Clearance between the valve and barrel
- Whether a hose needs room to attach
Support the bulkhead while tightening the valve. You do not want all the turning force transferred into the barrel wall.
Avoid using a long valve, pipe, or heavy hose assembly as a lever against the fitting. Extra support may be needed for heavier plumbing.
How to Leak-Test the Installation
Do not fill the entire barrel immediately.
Add enough water to cover the fitting and inspect the area closely.
Check:
- Around the flange
- Around the gasket
- Around the retaining nut area
- Any threaded connections attached to the fitting
A dry paper towel wiped around the connection can help reveal a very slow leak.
If the bulkhead itself leaks, drain the water below the fitting before adjusting it.
Do not simply keep tightening a plastic bulkhead. First check whether the gasket is flat, the hole is smooth, and the fitting is sitting squarely against the barrel.
Why a New Bulkhead Fitting May Leak
The Hole Is Too Large
The gasket needs enough solid barrel wall around the opening to form a seal.
If the hole is substantially oversized, tightening the nut may not solve the problem.
The Hole Is Rough
A burr or ridge underneath the gasket can prevent even contact.
Drain the barrel, remove the fitting, and smooth the sealing surface.
The Gasket Is Misplaced
Check the fitting manufacturer's installation arrangement.
Moving a gasket to the wrong side can cause leaks even when the nut feels tight.
The Gasket Is Twisted
A gasket should lie flat.
If it rolls, folds, or squeezes out from beneath the flange, loosen the fitting and reposition it.
The Barrel Wall Is Too Curved
A rigid bulkhead flange may not seal well against a sharply curved surface.
A different location or a fitting designed for the tank geometry may work better.
The Nut Is Too Tight
Overtightening can deform both the gasket and thin plastic barrel walls.
If the wall visibly bends around the fitting, excessive tightening may be part of the problem.
Installing a Bulkhead Fitting Near the Bottom of the Barrel
A low fitting is useful when you want to drain most of the stored water.
However, avoid drilling directly against the bottom edge.
You need room for:
- The fitting flange
- The retaining nut
- A valve or elbow
- Tools used during installation
Placing a fitting slightly above the barrel floor also leaves a small area where sediment can settle instead of immediately entering the outlet.
That can be useful because roof runoff may carry fine sediment into a rainwater system even when screens and other debris controls are used.
The remaining sediment should be removed during normal barrel cleaning.
Installing an Overflow Bulkhead
An overflow fitting lets excess water leave the barrel once storage is full.
Place it near the top while leaving enough solid barrel wall around the hole for the fitting flange.
The overflow pipe should carry water to a suitable drainage point rather than letting large amounts of water spill next to a foundation or into an unwanted area.
The overflow should also have enough capacity for the inflow expected from the roof collection system. A small overflow connection can become a restriction during heavy rain.
Keep openings screened where needed to reduce access for mosquitoes and debris.
Installing Bulkheads in Linked Rain Barrels
Bulkhead fittings can also connect several barrels.
The fittings and connecting pipe should line up without putting sideways force on the barrel walls.
Do not rely on the bulkheads to hold the weight of long pipes or several barrels pulling against each other.
Barrels should sit on stable, level supports. Flexible connections may help where slight movement or alignment differences are expected.
Remember that linked barrels become much heavier as they fill. Water weighs about 8.3 pounds per U.S. gallon, or about 1 kilogram per liter. The supporting surface must safely carry the total filled weight.
What If You Cannot Reach Inside the Barrel?
Traditional bulkhead fittings usually require access to both sides of the barrel wall.
That can be difficult if the barrel has only a small lid opening.
Possible solutions include choosing a fitting that can be installed through the available opening or using another tank connection method designed for installations without normal inside access.
Do not cut a large access hole into a barrel unless its design allows it. Removing structural sections can weaken some containers.
Bulkhead Fitting Maintenance
Bulkhead fittings do not need much routine work, but they should still be inspected.
Check them when cleaning the barrel and after freezing weather.
Look for:
- Drips
- Cracked plastic
- Loose plumbing
- Distorted gaskets
- Damage around the barrel wall
- Sediment blocking the outlet
Avoid repeatedly tightening a fitting that keeps leaking. A recurring leak usually means the fitting should be removed so the hole, gasket, and barrel wall can be inspected.
In freezing climates, drain and protect exposed plumbing as required for your system. Water trapped inside valves and fittings can expand when frozen and damage components.
A Good Bulkhead Installation Starts With the Hole
Installing a bulkhead fitting in a rain barrel is a manageable DIY job when you can safely reach both sides of the barrel.
The most important steps are simple: use the correct hole size, drill through a suitable part of the barrel, smooth the cut, install the gasket as designed, and tighten the fitting evenly without crushing the barrel wall.
Test the connection with a small amount of water before filling the barrel. If it leaks, find the cause instead of relying on more tightening or layers of sealant.
Frequently Asked Questions
Which side does the gasket go on for a bulkhead fitting?
It depends on the fitting design. On many bulkhead fittings, the gasket goes directly against the flange, with the barrel wall between the gasket and retaining nut. Follow the fitting manufacturer's instructions rather than assuming the gasket always goes inside the barrel.
How tight should a rain barrel bulkhead fitting be?
It should be tight enough to hold the fitting firmly and compress the gasket evenly. Avoid excessive force. Overtightening can distort the gasket, bend the barrel wall, damage threads, or crack plastic parts.
Do I need silicone around a bulkhead fitting?
Usually not if the fitting is designed to seal with a gasket and is installed correctly. Silicone should not be used to hide problems such as an oversized hole, damaged gasket, or uneven barrel surface.
What size hole do I drill for a bulkhead fitting?
Use the hole size specified for the exact fitting. Do not assume the required hole diameter is the same as the fitting's advertised pipe size. The body of the bulkhead is larger than its internal pipe opening.
Can I install a bulkhead fitting on a curved rain barrel?
Often, yes, if the curve is gentle enough for the flange and gasket to sit evenly. Strong curves can prevent a rigid fitting from sealing properly. Choose the flattest practical section of the barrel.
Why is my bulkhead fitting leaking?
Common causes include an oversized or rough hole, a twisted gasket, incorrect gasket placement, a strongly curved barrel wall, loose plumbing, or excessive tightening that has distorted the barrel or seal.
Can a bulkhead fitting be used for a rain barrel overflow?
Yes. A bulkhead fitting can provide a secure connection for an overflow pipe. The overflow system must still be large enough for expected inflow and should carry excess water to a suitable drainage location.
