Bulkhead Fittings for Aquarium Overflow Boxes | Reef Tank Plumbing

The diagram above shows a typical aquarium overflow box setup using a bulkhead fitting to create a sealed drain through the tank wall. Water flows from the display tank into the overflow chamber and exits through PVC plumbing connected to the bulkhead.

Bulkhead Fittings for Aquarium Overflow Boxes

Aquarium overflow drains typically use bulkhead fittings installed through the overflow box wall to connect PVC plumbing that carries water to the sump filtration system.

Aquarium overflow boxes rely on bulkhead fittings to safely move water from the display tank to the sump below. A properly installed bulkhead creates a watertight pass-through in the aquarium wall or overflow chamber, allowing plumbing to carry water away without leaks.

Bulkhead fittings are one of the most important components in reef aquarium plumbing. They allow hobbyists to build reliable gravity drains that maintain stable water levels while preventing spills or flooding.

At BulkheadFitting.com we supply heavy-duty ABS bulkhead fittings designed for aquariums, sumps, and filtration systems.

What Is an Aquarium Overflow Box?

An aquarium overflow box is a chamber that allows water to exit the main tank while maintaining a constant display water level.

Water flows over the overflow weir and enters the overflow box where it drains through plumbing to the sump or filtration system below the aquarium.

Bulkhead fittings are installed through the bottom or back wall of the overflow box to create a sealed outlet for the drain pipes.

This design allows aquariums to safely circulate water through external filtration systems while preventing the display tank from overflowing.

Why Bulkhead Fittings Are Used in Overflow Boxes

Bulkhead fittings serve several important roles in aquarium overflow systems:

• Create a watertight seal through the tank or overflow wall
• Allow PVC plumbing to connect to the drain system
• Maintain a stable display tank water level
• Prevent leaks around drilled holes in glass or acrylic
• Provide a secure mounting point for standpipes and drain plumbing

Without a properly installed bulkhead fitting, water would leak around the drilled hole in the aquarium.

Common Bulkhead Sizes for Aquarium Overflows

Most aquarium overflow boxes use larger bulkhead fittings to maximize water flow and reduce the chance of clogs.

Typical sizes include:

1.5" Bulkhead Fittings
Common in medium aquariums and many reef tank overflow systems.

2" Bulkhead Fittings
Used in larger aquariums where higher water flow is required.

Larger bulkhead fittings allow water to move more freely through the system, reducing noise and improving sump circulation.

Installing a Bulkhead in an Overflow Box

Installing a bulkhead fitting in an aquarium overflow box is straightforward when done correctly.

Basic steps include:

Drill the correct size hole in the overflow wall or tank panel
Insert the bulkhead fitting with the gasket on the water side
Tighten the nut on the outside of the tank
Connect PVC plumbing to the bulkhead outlet
Attach standpipes or strainers if required

The gasket should always be installed on the water side of the fitting to ensure a proper seal.

Before installing a bulkhead fitting in an overflow box, tank or sump, the correct hole size must be drilled through the tank wall.

Bulkhead drill hole size chart for aquarium overflow plumbing installations

Complete Bulkhead Installation Guide

Bulkhead Fittings for Reef Aquariums and Sumps

Bulkhead fittings are commonly used throughout reef aquarium systems, including:

• Overflow boxes
• Aquarium sump tanks
• Protein skimmer chambers
• Refugiums
• External filtration tanks

Using high-quality bulkhead fittings helps ensure long-term reliability in saltwater environments.

Shop Aquarium Bulkhead Fittings

Browse our selection of American-made ABS bulkhead fittings designed for aquarium plumbing and overflow systems.

• Slip x Slip Bulkhead Fittings
• Thread x Thread Bulkhead Fittings
• Thread x Slip Bulkhead Fittings

These heavy-duty bulkheads are thicker than standard Schedule 40 fittings and include durable EPDM gaskets for a reliable seal.

FAQ's

What size bulkhead is used for aquarium overflow boxes?

Most aquarium overflow systems use 1½" and 2" bulkhead fittings depending on the tank size and desired water flow. Larger bulkheads allow higher flow rates and reduce the chance of drain restrictions.