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For most rainwater tanks, a polypropylene tank connector with an EPDM rubber gasket is the best all-around choice. It resists rust, handles outdoor water use well, and works well with many polyethylene plastic tanks.
However, the best material depends on the tank, the water use, and how much stress the fitting will carry. Stainless steel can be better for demanding installations, while drinking-water systems need fittings specifically approved for potable water.
What Is a Tank Connector?
A tank connector is a fitting that lets water pass through the wall of a tank. It may connect the tank to:
- A valve
- A hose
- An irrigation line
- A pump suction line
- An overflow pipe
- Another storage tank
Many tank connectors are also called bulkhead fittings. A bulkhead fitting passes through a hole in the tank wall. A gasket seals around the hole while a nut holds the fitting in place.
The fitting material matters because the connector stays in contact with water and may spend years outdoors.
Best Material for Most Plastic Rainwater Tanks
For a typical polyethylene rainwater tank, polypropylene is often the most practical material.
Polypropylene tank connectors have several advantages:
- They do not rust.
- They resist many common chemicals.
- They are light, so they put less stress on a plastic tank wall.
- They work well in wet outdoor conditions.
- They are widely used with polyethylene tanks.
- They can be easier to install without damaging the tank than a heavy metal fitting.
A good-quality polypropylene connector paired with an appropriate EPDM gasket is usually suitable for garden watering, irrigation, tank transfer lines, and other non-potable rainwater uses.
Polypropylene and polyethylene are different plastics, but they are commonly used together in water-storage systems.
Is Stainless Steel Better?
Stainless steel is stronger than polypropylene, but that does not automatically make it better for every tank.
Stainless steel may make sense when the connector must handle:
- Frequent pipe movement
- Large valves
- Heavy plumbing
- Higher mechanical loads
- Harsh outdoor exposure
- Situations where plastic threads could be damaged
Grade 316 stainless steel is commonly chosen where corrosion resistance is especially important.
The problem is that a strong metal fitting can still damage a plastic tank. A heavy valve or rigid pipe can place considerable force on a thin tank wall. Overtightening the fitting can also deform or crack some tanks.
If you use a metal fitting on a plastic tank, support heavy valves and piping separately rather than expecting the tank wall to carry their full weight.
Metal tanks require extra care. Putting different metals together in a wet environment can contribute to galvanic corrosion. Follow the tank manufacturer's recommendations for compatible fittings, gaskets, and isolation where needed.
What About Brass Tank Connectors?
Brass is durable and easy to connect to common plumbing parts. It can work well in some tank systems.
For ordinary garden-water systems, however, brass may offer little advantage over a good plastic bulkhead fitting.
There is another concern if the water could be used for drinking.
In the United States, fittings used in plumbing that supplies water for human consumption must meet federal lead-content requirements. The Safe Drinking Water Act defines "lead free" for most wetted plumbing components as no more than a 0.25% weighted average lead content across wetted surfaces.
Do not assume that any brass fitting is suitable for drinking water simply because it is labeled "brass" or "lead free."
What Is Best for a Potable Water Tank?
Potable means suitable for drinking.
For a potable-water system, the material name alone is not enough. A polypropylene, stainless steel, or brass connector may be suitable, but the specific fitting and its water-contact materials should be approved for drinking-water use.
NSF/ANSI/CAN 61 covers health effects from materials and components that contact drinking water, including fittings, pipes, gaskets, and other system parts.
NSF/ANSI/CAN 372 deals specifically with lead content. It does not by itself cover every possible health effect from a drinking-water fitting.
For a rainwater system intended to supply drinking water, check the complete water path. That includes the:
- Roof and collection surfaces
- Tank
- Tank connector
- Gaskets
- Pipes and valves
- Pump
- Treatment equipment
Collected roof runoff should not be assumed safe to drink simply because the tank and fittings are potable-water rated. Drinking-water use requires suitable collection, treatment, maintenance, current laboratory testing, and compliance with applicable local requirements.
The Gasket Material Matters Too
The tank connector itself is only part of the seal. The gasket is just as important.
For ordinary water tanks, EPDM rubber is often a good choice because it handles water, weather, ozone, and outdoor conditions well.
The gasket should be compatible with both the stored water and the fitting.
For drinking-water systems, use a gasket specifically approved for potable-water contact. NSF/ANSI/CAN 61 includes joining and sealing materials such as gaskets within its scope.
Do not use a random rubber washer simply because it fits.
Polypropylene vs Stainless Steel vs Brass
| Material | Best suited for | Main advantage | Main concern |
|---|---|---|---|
| Polypropylene | Most plastic rainwater tanks | Corrosion resistant and lightweight | Threads can be damaged by overtightening |
| 316 stainless steel | Heavy-duty or demanding installations | Very strong and corrosion resistant | Heavy and can stress plastic tank walls |
| Brass | Conventional plumbing connections | Strong and easy to connect | Potable systems require suitable lead-free certification |
| PVC | Some tank and pipe systems | Corrosion resistant and easy to connect to PVC pipe | Compatibility and pressure limits depend on the fitting |
| Nylon | Some small tank fittings | Lightweight and inexpensive | Water absorption and outdoor durability vary by grade |
There is no single material that is best under every condition.
Match the Connector to the Tank
Before choosing a fitting, check what the tank manufacturer allows.
Consider suitable materials for filter housings to assess a water-safety plan appropriate for the intended purpose.
A connector must match several things at once:
Tank Wall Material
A rigid metal fitting may not be ideal for a thin or flexible plastic wall. A lightweight plastic bulkhead fitting is often easier on polyethylene tanks.
Hole Size
Tank connectors require a specific hole diameter. A fitting described as 1 inch does not necessarily need a 1-inch hole.
The nominal fitting size usually describes the pipe connection, not the hole you must drill.
Check the fitting dimensions before cutting the tank.
Thread Type
Make sure the connector matches the valve, pipe, hose adapter, or pump line you intend to attach.
Do not assume two fittings will connect just because both are marked with the same nominal size. Thread standards can differ.
Water Use
A connector suitable for garden irrigation is not automatically suitable for drinking water.
For non-potable rainwater, corrosion resistance and mechanical compatibility may be the main concerns. For potable water, certification of the complete water-contact assembly matters as well.
Pipe Weight
Long rigid pipes, large valves, pumps, and filters can put sideways force on a tank connector.
Support heavy plumbing independently. The tank wall should not act as a pipe support.
Do Tank Connectors Need Thread Tape?
It depends on which joint you are sealing.
The gasket normally seals the bulkhead fitting against the tank wall. Adding thread tape around the fitting where the gasket seals usually does not fix a poor gasket seal.
Thread sealant may be needed on tapered threaded plumbing connections attached to the connector, depending on the fitting manufacturer's instructions.
Do not keep tightening a leaking bulkhead fitting indefinitely. Too much force can crush the gasket, distort the fitting, or damage the tank wall.
If a new connection leaks, check:
- Whether the gasket is in the correct position.
- Whether the sealing surfaces are clean.
- Whether the hole is the correct size and shape.
- Whether the fitting is sitting squarely against the tank.
- Whether the gasket material is compatible.
- Whether the fitting has been overtightened.
A cracked or badly distorted tank wall may require more than simply replacing the connector.
Best Choice for Common Rainwater Systems
For a plastic rain barrel or polyethylene storage tank, a polypropylene bulkhead fitting with an appropriate EPDM gasket is usually the simplest choice.
For a large cistern with heavy external plumbing, stainless steel may provide greater mechanical strength, provided the tank is designed for the fitting and the piping is properly supported.
For a drinking-water system, choose a complete fitting and gasket assembly certified for the intended potable-water use rather than choosing by material alone.
For a metal tank, check the manufacturer's recommendations before mixing fitting metals. Preventing corrosion at the connection can be more important than simply choosing the strongest fitting.
The main goal is not to find the toughest material. It is to use a connector that matches the tank, seals correctly, carries the expected load, and is suitable for the water's intended use.
Frequently Asked Questions
Is polypropylene good for tank fittings?
Yes. Polypropylene is a good material for many rainwater tank fittings because it does not rust, is lightweight, and works well in wet outdoor conditions. It is especially practical for polyethylene plastic tanks.
Is brass or plastic better for a water tank?
Plastic is often better for a normal polyethylene rainwater tank because it is lightweight and corrosion resistant. Brass may be useful when stronger plumbing connections are needed. For drinking-water systems, any brass fitting should meet applicable potable-water and lead-content requirements.
Can I use a stainless steel fitting on a plastic tank?
Yes, if the tank is designed to accept it. Avoid overtightening the fitting, and support heavy valves or pipes separately so they do not place excessive force on the plastic tank wall.
What gasket is best for a rainwater tank connector?
EPDM is commonly a good choice for water tanks because it handles water and outdoor exposure well. For potable systems, use a gasket specifically approved for drinking-water contact.
Can I use PVC fittings on a rainwater tank?
PVC fittings can work in many rainwater systems, especially when the connected pipe is also PVC. Check the fitting's pressure, temperature, UV exposure, and tank compatibility requirements rather than assuming every PVC fitting is interchangeable.
Does a potable tank need a potable tank connector?
If the stored water will be used for drinking, all materials that contact the water should be suitable for that use. A potable-rated tank does not make an unsuitable connector, gasket, valve, or pipe safe for drinking-water service.
Should a tank connector be metal or plastic?
For most plastic rainwater tanks, a quality plastic connector such as polypropylene is usually sufficient. Metal fittings are useful when greater mechanical strength is needed, but the tank wall and attached plumbing must be able to handle the extra load.
