Moroso 85406 Polyethylene Breather Tank Catch Can with -6AN Inlet

Single -6AN Male Inlet

Moroso identifies part number 85406 as:

Breather Tank / Catch Can — Polyethylene — -6AN Male Fitting

The -6AN connection makes this version useful for systems already plumbed around relatively compact AN hose.

That’s different from the large -10AN, -12AN and -16AN plumbing commonly found on high-volume racing crankcase and vacuum-pump systems.

Choose the fitting size according to the airflow requirements of the system.

Don’t Confuse -6AN With Tank Diameter

Some marketplace data describes the 85406 as having a 6-inch-diameter tank.

That appears to be a data interpretation problem.

The important published specification is:

Inlet: -6AN male

The number 6 in -6AN refers to the AN fitting size.

AN sizing is traditionally based on sixteenths of an inch.

Therefore:

-6AN = 6/16 nominal tube-size reference = 3/8 inch

That does not mean every internal hose dimension is exactly 3/8 inch, and it definitely doesn’t mean the tank itself is six inches wide.

For Pro Street Online, I would remove “6 In. Dia Tank” from the product title unless you have separate Moroso documentation proving that dimension.

Lightweight Polyethylene Construction

The Moroso 85406 uses a black polyethylene tank body.

Polyethylene has several advantages for a simple remote breather tank:

• Low weight
• Corrosion resistance
• No need for a painted exterior
• Lower cost than elaborate billet construction
• Suitable durability for compatible racing applications

For a functional race build where saving weight and money matters more than having another polished aluminum object under the hood, that’s a sensible combination.

Filtered Breather

The tank uses a breather filter mounted at the top.

The filter allows gases to vent while helping control contamination at the vent opening.

This creates a basic remote-breather arrangement:

FLUID/VAPOR ENTERS BELOW

↓

FLUID COLLECTS IN TANK

↓

GAS VENTS THROUGH FILTER

The tank should generally be mounted upright so collected fluid remains in the lower portion rather than saturating the breather.

Why Use a Remote Breather Tank?

Vented automotive components can carry more than air through their vent lines.

Depending on the application, the vent stream may contain:

• Oil mist
• Gear oil
• Condensation
• Crankcase vapor
• Other fluid droplets

Routing the vent into a remote catch tank gives that material somewhere to collect.

That’s particularly valuable on competition vehicles where fluid escaping onto:

• Tires
• Brakes
• Exhaust
• Track surface

is considerably more serious than simply making the engine compartment dirty.

Useful for Crankcase Ventilation

The 85406 can be used in appropriately designed crankcase ventilation systems where a -6AN vent line provides sufficient flow.

Crankcase blow-by contains combustion gases and suspended oil.

A remote tank can help keep oil mist contained rather than allowing it to collect around the engine compartment.

However, -6AN is relatively modest for high-output crankcase ventilation.

Large-displacement racing engines may require substantially larger plumbing.

Don’t choose hose size based solely on whichever fitting happens to be easiest to route.

Crankcase Flow Requirements Matter

A breather system needs enough flow capacity to prevent excessive crankcase pressure.

Insufficient ventilation can contribute to:

• Oil leaks
• Dipstick displacement
• Oil pushed through seals
• Gasket leakage
• Increased crankcase pressure

A -6AN tank may be appropriate for some applications while being too restrictive for others.

Large racing engines commonly use -10AN, -12AN, -16AN or multiple vent connections depending on the system.

Match the breather to the engine rather than assuming one size fits everything.

Useful for Transmission Venting

Remote catch tanks can also be useful on racing transmissions.

Transmission fluid expands as temperature increases.

Under hard acceleration, braking and cornering, fluid can also move aggressively inside the case.

A remote vent line allows the transmission to breathe while moving the vent termination away from the transmission itself.

If a small amount of fluid travels up the vent line, the catch tank gives it somewhere to collect.

Useful for Differential Venting

The same principle applies to racing differentials.

Gear oil becomes hot during operation.

As temperature rises, internal pressure needs to equalize.

A remote breather line can relocate the vent higher in the vehicle and provide additional fluid containment.

A basic arrangement might be:

DIFFERENTIAL VENT → -6AN LINE → MOROSO 85406

The correct routing depends on the axle and vehicle.

Keep the Tank Above the Vent Source When Practical

Remote vent systems generally benefit from sensible hose routing.

Where the application permits, route the line so gravity can help keep bulk fluid in the original component.

Avoid creating low spots where fluid can pool unnecessarily.

Also avoid routing vent hoses:

• Near exhaust heat
• Against sharp sheet metal
• Around moving suspension components
• Where the hose can kink
• Where debris can damage it

Secure the hose at appropriate intervals.

Mount the Tank Upright

The breather is located at the top for a reason.

Mount the 85406 vertically whenever the application allows.

This keeps collected fluid toward the bottom of the tank and helps prevent saturation of the breather element.

It also makes inspection and servicing easier.

Check the Tank Regularly

A catch tank only has useful capacity while it isn’t full.

Check it periodically.

How often depends on the application.

A differential vent tank might collect very little during normal operation.

A crankcase breather on an engine with significant blow-by may collect considerably more.

Initially inspect the tank frequently until you understand the normal accumulation rate.

Sudden Fluid Accumulation Is Diagnostic Information

Pay attention when a breather tank suddenly begins collecting more fluid than usual.

On an engine, that could point toward:

• Increased blow-by
• Ring-seal problems
• Excessive oil near the vent pickup
• Poor internal baffling

On a transmission or differential, unusual fluid collection might indicate:

• Overfilling
• Excessive operating temperature
• Aggressive fluid aeration
• Poor vent-line placement

Don’t just empty the tank forever without investigating why its behavior changed.

Can Be Modified for a Second Vent Connection

Moroso’s polyethylene breather-tank design is intended to accommodate different inlet arrangements within the product family, and the supplied product information notes that the tank can be modified for an additional fitting when dual vent hoses are required.

If modifying the tank, use components compatible with the polyethylene construction and the fluid being handled.

More importantly, make sure the modification doesn’t create leaks or weaken the mounting area.

For applications that already require dual large-volume connections, buying a purpose-built dual-inlet tank may be a cleaner solution.

Moroso Offers Several Inlet Sizes

The 85406 belongs to a family of polyethylene breather tanks with different AN inlet sizes.

Moroso’s current catalog identifies:

85400 — -12AN male fitting

85402 — -10AN male fitting

85404 — -8AN male fitting

85406 — -6AN male fitting

This is useful for Pro Street Online because all four products can be merchandised together.

The primary difference is the inlet size.

85406 vs 85404

Moroso 85406

Inlet: -6AN

Best suited to applications requiring the smaller connection.

Moroso 85404

Inlet: -8AN

Provides a larger connection for systems requiring additional vent capacity.

85406 vs 85402

Moroso 85406

Inlet: -6AN

Moroso 85402

Inlet: -10AN

The -10AN version is a better starting point for applications requiring substantially more ventilation flow.

85406 vs 85400

The 85400 steps up to a -12AN male connection.

That’s a substantial increase over the -6AN connection on the 85406 and may be more appropriate for higher-volume crankcase applications.

Again, bigger isn’t automatically better.

Select the connection based on actual system requirements.

Moroso 85406 vs 85469

These two Moroso tanks serve similar general purposes but target very different plumbing requirements.

Moroso 85406

Construction: Black polyethylene
Inlet: Single -6AN
Purpose: Lightweight remote vent/catch tank

Moroso 85469

Construction: Aluminum
Connections: Dual -12AN
Purpose: High-flow racing breather tank for crankcase, vacuum-pump, dry-sump and related applications

A dual -12AN racing engine system needs dramatically more plumbing capacity than a single -6AN vent.

These products shouldn’t be presented as direct equivalents.

Moroso 85406 vs New Billet Breather Tanks

Moroso introduced a newer family of billet breather tanks in 2026 with single- and dual-inlet configurations from -6AN through larger sizes. Those tanks use black-anodized billet construction, internal baffling and replaceable fittings.

The 85406 remains the simpler polyethylene approach.

That gives customers a useful choice between:

Lightweight functional polyethylene tank

and

Premium billet baffled tank

depending on budget, packaging and intended use.

Universal Fitment

The Moroso 85406 should be classified as universal, not vehicle-specific.

Compatibility depends on:

• Vent-line size
• Available mounting space
• System airflow requirements
• Hose routing
• Intended fluid
• Racing application

It isn’t selected according to whether the car is a Camaro, Mustang, Civic or Corvette.

For ecommerce data, use:

Fitment Type: Universal

Inlet: -6AN male

Tank Type: Remote breather/catch tank

Construction: Polyethylene

One-Quart Capacity

The supplied product information identifies the 85406 as a 1-quart-capacity tank.

That is a reasonable catalog attribute to retain if it comes from your distributor data, but I would keep it separate from Moroso’s directly verified specifications because Moroso’s current indexed catalog listing primarily identifies the 85406 by construction and -6AN inlet size.

In other words:

1-quart capacity — distributor/catalog specification

-6AN male fitting — directly supported by current Moroso catalog

This avoids presenting marketplace data as though it came directly from Moroso.

Package Dimensions

Your supplied package data lists:

Package Height: 12.7 cm / 5.0 inches

Package Length: 39.624 cm / 15.6 inches

Package Width: 11.938 cm / 4.7 inches

Package Weight: 1.4 pounds

These are shipping-package measurements.

They should not be used as installed tank dimensions.

Made in the USA

Moroso’s published origin documentation identifies its polyethylene breather-tank family as USA origin.

That matches the country-of-origin information supplied with the product.

Moroso 85406 Specifications

Part Number: 85406

Product: Breather Tank / Catch Can

Construction: Black polyethylene

Inlet: Single -6AN male fitting

Breather: Top-mounted filtered breather

Capacity: 1 quart, according to supplied distributor data

Fitment: Universal

Application: Remote vent/catch tank for compatible automotive and racing systems

Country of Origin: United States

Package Height: 12.7 cm / 5 inches

Package Length: 39.624 cm / 15.6 inches

Package Width: 11.938 cm / 4.7 inches

Package Weight: 1.4 lb

Who Should Buy the Moroso 85406?

The Moroso 85406 is useful when a lightweight universal remote breather tank with a -6AN connection matches the vent system being built.

Potential applications include:

• Race cars
• Project cars
• Transmission vent systems
• Differential vent systems
• Appropriate crankcase vent systems
• Custom racing ventilation
• Pro Street builds

It is particularly attractive when weight, simplicity and cost matter more than polished billet construction.

Who Should Choose a Larger Tank Connection?

If the application requires substantial crankcase airflow, look at Moroso’s larger-inlet breather tanks.

The same polyethylene family includes -8AN, -10AN and -12AN configurations.

Moroso also offers aluminum and billet tanks with larger and/or dual connections.

For the racing vacuum-pump system we’ve been building around the Moroso 22641, a larger purpose-designed tank such as the dual -12AN Moroso 85469 is generally the more logical type of component.

The 85406 occupies a different niche.

Final Verdict

The Moroso 85406 Polyethylene Breather Tank is a simple, lightweight solution for remote vent applications requiring a single -6AN male connection.

Its black polyethylene construction keeps weight down, while the top-mounted filtered breather gives oil mist or other vented fluid a remote collection point instead of allowing it to escape directly around the vehicle.

The most important purchasing consideration is sizing.

Don’t interpret -6AN as a six-inch tank.

Don’t select a small vent connection for an engine that requires substantially more crankcase airflow.

And don’t buy the largest fitting available simply because bigger AN numbers make the engine compartment look more serious.

Match the breather tank to the system.

That’s considerably cheaper than discovering your vent system was undersized when the engine begins finding its own creative ways to relieve crankcase pressure.