Illegal S traps are a common plumbing problem that plumbers find in older homes and poorly done remodels. Many homeowners are unaware that an S trap can cause serious drainage and sewer gas issues. Professional plumbers regularly remove and replace these traps to bring plumbing systems up to code and protect indoor air quality.
At Roto-Rooter, plumbers see S traps during routine drain cleaning and inspections. Understanding why S traps are illegal helps homeowners make informed decisions and avoid recurring plumbing problems.
What Is an S Trap in Plumbing
An S trap is a drain configuration shaped like the letter S. It typically drops straight down through the floor after the curve of the trap. While it may look similar to a P trap, the vertical drop is what makes it unsafe.
The purpose of any plumbing trap is to hold a small amount of water that blocks sewer gases from entering the home. Licensed plumbers know that the shape and venting of the trap are critical for this water seal to remain intact.
Why S Traps Are Illegal
S traps are illegal under modern plumbing codes because they are prone to siphoning. When water flows quickly through an S trap, it can pull all the water out of the trap. Once the trap dries out, sewer gases can enter the home.
Plumbers frequently report these issues with S traps:
• Loss of the water seal
• Sewer odors coming from sinks or tubs
• Gurgling drains
• Increased risk of bacteria and methane gas entering the home
Because of these risks, plumbers are required to remove S traps when discovered during plumbing work.
Difference Between an S Trap and a P Trap
A P trap has a horizontal outlet that connects to a vented drain line in the wall. This design prevents siphoning and keeps the trap full of water.
Plumbers prefer P traps because they are code compliant and reliable. The key difference is venting. An S trap lacks proper venting, while a P trap works with a vent system to maintain pressure balance.
How Plumbers Identify an Illegal S Trap
Experienced plumbers can quickly spot an S trap during a visual inspection. Common locations include:
• Bathroom sink drains in older homes
• Kitchen sinks that drain through the floor
• Basement utility sinks
• DIY plumbing installations
If the drain pipe curves downward and disappears into the floor instead of running horizontally to a wall, plumbers will likely identify it as an illegal S trap.
Dangers of Keeping an S Trap
Keeping an S trap in place can lead to more than just unpleasant odors. Plumbers warn homeowners about long term risks such as:
• Exposure to sewer gases
• Drainage problems and slow drains
• Potential health issues from airborne contaminants
• Code violations that affect home inspections and resale
Professional plumbers recommend correcting the issue as soon as it is discovered.
How Plumbers Fix an S Trap
Fixing an S trap usually involves converting it to a properly vented P trap. Plumbers may:
• Re route the drain to connect to a wall vent
• Add an approved venting solution where allowed
• Replace outdated plumbing materials
A licensed plumber will ensure the repair meets local plumbing codes and functions correctly for the long term.
When to Call a Professional Plumber
If you notice sewer odors, gurgling drains, or recurring clogs, plumbers recommend scheduling an inspection. Attempting to fix an S trap without proper knowledge can create additional plumbing problems.
Roto-Rooter plumbers have the experience and equipment to identify illegal S traps and replace them safely. Calling a professional plumber ensures your plumbing system remains code compliant and odor free.
Roto-Rooter provides professional plumber services for homes with illegal S traps throughout California, including plumbers in Sacramento, plumbers in Bakersfield, plumbers in Fresno, among other locations where plumbers frequently encounter outdated drain configurations during inspections and repairs. Our licensed plumbers identify illegal S traps, explain why they cause sewer gas and drainage problems, and replace them with properly vented and code compliant solutions to protect indoor air quality and ensure long term reliability.
Trust Plumbers to Handle Illegal S Traps
Illegal S traps are more than an outdated plumbing design. They are a proven cause of sewer gas leaks and drainage issues. Plumbers across the industry agree that replacement is the only reliable solution.
If you suspect your home has an S trap, contact Roto-Rooter to have a licensed plumber inspect your plumbing system and recommend the proper fix.