What is the minimum trap size required by plumbing codes for serving an automatic clothes washer?

What is the minimum trap size required by plumbing codes for serving an automatic clothes washer?

• A. 1 inch
• B. 2 inches
• C. 1-1/2 inches
• D. 3 inches

Answer: (B)

When a fixture dumps wastewater into the drain, the trap must be big enough to keep the trap seal from being sucked out by the rush of water. Automatic clothes washers discharge a large volume of water quickly, so a larger trap helps prevent siphoning and preserves the seal against sewer gases. The 2-inch trap size is the minimum that codes require for a clothes washer because it provides sufficient capacity and reduces the risk of losing the trap seal under washer discharge. Smaller traps, like 1-1/2 inches or 1 inch, are common for sinks but are more prone to siphonage with a washer’s heavy flow. A 3-inch trap would be larger than necessary for this fixture, so the standard minimum is 2 inches.

When a fixture dumps wastewater into the drain, the trap must be big enough to keep the trap seal from being sucked out by the rush of water. Automatic clothes washers discharge a large volume of water quickly, so a larger trap helps prevent siphoning and preserves the seal against sewer gases. The 2-inch trap size is the minimum that codes require for a clothes washer because it provides sufficient capacity and reduces the risk of losing the trap seal under washer discharge. Smaller traps, like 1-1/2 inches or 1 inch, are common for sinks but are more prone to siphonage with a washer’s heavy flow. A 3-inch trap would be larger than necessary for this fixture, so the standard minimum is 2 inches.