As an affiliate, we may earn a commission from qualifying purchases. We get commissions for purchases made through links on this website from Amazon and other third parties.
A bulkhead fitting lets you make a watertight connection through the wall of a rain barrel, IBC tote, or water tank. It is often used for outlets, drains, valves, overflow pipes, and tank-to-tank connections.
To fit one correctly, you need the right hole size, a smooth sealing surface, and even pressure on the gasket. The most common mistake is cutting the hole too large or tightening the fitting too much.
What Is a Bulkhead Fitting?
A bulkhead fitting is a connector that passes through the wall of a container.
Most bulkhead fittings have:
- A flanged body that passes through the hole
- A rubber or flexible gasket
- A large retaining nut
- Threads for attaching a pipe, valve, hose adapter, or other fitting
The flange and nut clamp the tank wall between them. The gasket creates the water seal.
Bulkhead fittings are useful because they do not depend on glue or sealant alone to stop leaks.
Before You Start
Check the fitting and the tank before drilling anything.
You need to know:
- The required hole diameter
- Whether the fitting will sit on a flat surface
- Which side the gasket goes on
- Whether you can reach both sides of the tank wall
- What pipe or valve will connect to the fitting
Do not choose the drill size based only on the advertised pipe size.
For example, a fitting sold for a certain pipe size normally needs a larger hole because the body of the bulkhead must pass through the tank wall.
Use the hole diameter listed by the fitting manufacturer when available.
Choose a Good Location
Pick a part of the tank wall that is as flat as possible.
A flat surface gives the gasket even contact around the whole opening.
Avoid installing the fitting:
- Across a molded seam
- On a rib or raised section
- Very close to the bottom edge
- On a sharply curved surface
- Where the nut cannot be reached
- Where attached plumbing will put heavy sideways force on the fitting
Rain barrels often have curved walls. Look for a molded flat area if the barrel has one.
IBC totes may also have ribs and structural sections that make poor sealing surfaces.
If the outlet is being installed near the bottom, leave enough room to turn the nut and attach the valve or pipe.
Make Sure the Tank Is Safe to Drill
Empty the tank before drilling whenever practical.
Do not drill into a container that holds an unknown substance, fuel, solvent, chemical, or anything that could produce dangerous fumes.
For large cisterns, do not climb inside the tank to install a fitting unless the tank is specifically designed for safe entry and proper confined-space procedures are being followed.
Many small rain barrels and totes can be fitted without entering them.
How to Fit a Bulkhead Fitting
1. Confirm the Required Hole Size
Measure the bulkhead body and check the manufacturer's instructions.
The hole must be large enough for the threaded body to pass through without forcing it, but small enough for the flange and gasket to fully cover the opening.
Do not guess based on nominal pipe size.
2. Mark the Center of the Hole
Mark the center point with a permanent marker.
Check the position again before drilling.
Make sure there is enough clearance around the hole for:
- The gasket
- The flange
- The retaining nut
- A wrench or your hand
- Any valve or pipe attached later
This is especially important near the bottom of a barrel.
3. Drill a Pilot Hole if Needed
Some hole saws use a center drill bit.
Keep the drill square to the tank wall so the hole is not cut at an angle.
Support lightweight plastic containers so they do not flex or move while you drill.
4. Cut the Opening
Use the correct hole saw or cutting tool for the tank material.
Work slowly. Too much pressure can crack brittle plastic or make the hole rough.
Once the cut is complete, remove the round piece carefully.
5. Clean the Hole
Remove plastic shavings and any rough edges.
The gasket needs to sit against a smooth surface.
A raised burr can create a small channel where water leaks past the gasket.
Do not remove so much material that you enlarge the hole.
6. Install the Gasket in the Correct Position
Bulkhead designs vary, so follow the instructions supplied with your fitting.
On many common designs, the gasket sits against the flange and sealing surface rather than against the retaining nut. The flanged side is often installed inside the tank, but that is not a universal rule.
Do not automatically add extra washers, silicone, or thread tape around the gasket.
A properly designed bulkhead normally seals by compressing its gasket against the tank wall.
7. Insert the Bulkhead Body
Push the body through the hole without forcing it.
The gasket should stay flat.
Check that it has not:
- Folded
- Twisted
- Slipped out of position
- Caught on a rough edge
The flange should sit evenly against the tank.
8. Install the Retaining Nut
Thread the nut onto the bulkhead body.
Start it by hand so you do not cross-thread it.
Tighten until the fitting is secure and the gasket is evenly compressed.
Do not keep tightening simply because the nut can still turn.
Over-tightening can distort the gasket, damage the fitting, or deform a thin plastic barrel wall.
Follow the manufacturer's tightening instructions if they provide them.
Should You Use Silicone on a Bulkhead Fitting?
Usually, a standard gasketed bulkhead should not need silicone to create its main seal.
Adding sealant can sometimes cause problems. A slippery gasket may move as the nut is tightened, or the sealant may make future removal difficult.
If a fitting leaks, first check:
- Hole size
- Gasket position
- Burrs around the hole
- Uneven tightening
- Curvature of the tank
- Cracks around the opening
Do not use sealant to compensate for a badly sized or damaged hole unless the fitting manufacturer specifically allows that installation method.
Which Way Should a Bulkhead Fitting Face?
With key facts about another name for a bulkhead fitting, you can compare component compatibility before materials are finalized.
The answer depends on its design.
A common arrangement is:
Inside tank: flange and gasket Tank wall: between the fitting parts Outside tank: retaining nut
This arrangement often makes sense because the water pressure pushes the gasket and flange against the tank wall.
However, some fittings are designed differently. Always check the fitting instructions before deciding which direction it should face.
The important point is that the gasket must be placed where the manufacturer intends it to create the seal.
Connecting a Valve or Pipe
Once the bulkhead is secure, you can attach the next part of the system.
That might be:
- A ball valve
- A hose adapter
- PVC pipe
- An overflow pipe
- A garden irrigation line
- A pipe connecting two storage tanks
Check the thread type before attaching anything.
A connection that looks close in size may still have different threads.
For threaded plumbing connections, thread seal tape or another approved thread sealant may be needed on the pipe threads. That is separate from the gasket that seals the bulkhead to the tank wall.
Avoid using the bulkhead as a support for heavy plumbing.
Long pipes and large valves can put sideways force on the tank wall. Support them separately when needed.
How Tight Should a Bulkhead Fitting Be?
It should be tight enough that the gasket forms an even seal, but not so tight that the tank or gasket is distorted.
Thin plastic barrels are especially easy to deform.
Signs of excessive tightening include:
- The tank wall bending inward
- The gasket squeezing out from under the flange
- The fitting becoming crooked
- Cracking sounds
- Visible stress marks in the plastic
If the manufacturer gives a torque value or tightening procedure, use that instead of a general rule.
Test the Fitting Before Filling the Tank
Do not fill a large tank completely right away.
Add a small amount of water first so the water level is above the fitting.
Dry the outside around the bulkhead and watch for moisture.
If it stays dry, add more water and check again.
Remember that pressure at a fitting increases as the water level above it rises. A connection that stays dry under a few inches of water should still be checked after the tank reaches its normal operating level.
What to Do if the Bulkhead Leaks
Do not immediately tighten the nut as hard as possible.
First identify where the leak is coming from.
Leak Between the Bulkhead and Tank
Check for:
- A twisted gasket
- Dirt under the gasket
- A rough hole
- A hole that is too large
- A curved sealing surface
- An incorrectly positioned gasket
The fitting may need to be removed and installed again.
Leak From a Threaded Pipe Connection
The bulkhead gasket may be fine.
Instead, check the connection between the pipe or valve and the bulkhead threads.
Make sure the threads match and that the correct thread sealant is being used where required.
Leak From a Crack Around the Hole
Stop filling the tank.
A crack may continue spreading as the water load increases.
Replacing or properly repairing the tank may be safer than trying to tighten the fitting further.
Installing a Bulkhead on a Curved Rain Barrel
Curved walls can make installation harder because a flat flange is trying to seal against a rounded surface.
A small fitting may work on a gently curved section because the wall can flex slightly.
Large fittings need a larger flat sealing area and may not seal well on a strongly curved surface.
Whenever possible, use:
- A factory-made flat section
- A flat side panel
- A location with the least curvature
Do not force a large rigid fitting onto a surface that becomes badly distorted when tightened.
Installing a Bulkhead on an IBC Tote
IBC totes have both an inner plastic bottle and an outer metal cage.
Choose a location where the fitting:
- Clears the cage
- Sits on a suitable part of the plastic bottle
- Can be reached for tightening
- Will not interfere with the pallet or frame
- Can support the planned plumbing connection
Think about pipe routing before drilling.
A bulkhead that fits the tote but leaves no room for a valve is not very useful.
Also confirm that the tote is suitable for its intended water use. The previous contents of a used IBC tote matter, especially when collected water will be used around food crops or for household purposes.
Plan for Maintenance
Bulkhead fittings should be checked from time to time.
Look for:
- Drips
- Loose plumbing
- Cracked plastic
- Gasket deterioration
- Movement caused by attached pipes
- Freeze damage
Freezing water can damage valves, pipes, fittings, and tank walls.
In freezing climates, design the system so vulnerable plumbing can be drained or otherwise protected before freezing weather.
Frequently Asked Questions
What size hole do I drill for a bulkhead fitting?
Use the hole diameter specified by the fitting manufacturer. Do not use the nominal pipe size as the hole size because the bulkhead body is usually larger than the pipe connection.
Does the gasket go inside or outside the tank?
It depends on the bulkhead design. On many fittings, the gasket sits next to the flange, which is often installed inside the tank. Follow the manufacturer's instructions rather than assuming all bulkheads use the same arrangement.
Do bulkhead fittings need silicone?
Most gasketed bulkhead fittings are designed to seal without silicone. If one leaks, check the gasket, hole size, surface condition, and installation before adding sealant.
Can I install a bulkhead fitting on a curved rain barrel?
Sometimes. Small fittings may seal on gently curved plastic, but large fittings need a wider flat sealing surface. A molded flat section is usually the better location.
Can you overtighten a bulkhead fitting?
Yes. Too much tightening can squeeze the gasket out of place, deform the tank wall, damage threads, or crack the fitting.
Why is my new bulkhead fitting leaking?
Common causes include a twisted gasket, rough hole edge, oversized hole, curved tank wall, incorrect gasket position, or excessive tightening. A leak from the attached pipe threads is a separate problem from the bulkhead-to-tank seal.
Can a bulkhead fitting be used near the bottom of a water tank?
Yes, and that is a common location for drains and outlets. Leave enough space to tighten the nut and install the valve or pipe. Remember that fittings near the bottom experience the greatest water pressure because the full water depth is above them.
