3 Surprising Reasons Your Sink Smells Like Rotten Eggs And What To Do

Having your kitchen sink emit a rotten egg odor can be unpleasant and embarrassing. You frantically scrub the sink, only to sniff that nauseating sulfur stench rising again. Before you panic, arm yourself with a little DIY troubleshooting knowledge.

Reason 1: Clogged or Partially Clogged Drain

The most common source of a sewer gas smell from your sink happens when water flow slows. Drain clogs prevent the smooth drainage of water, allowing bacteria growth inside the pipes and P-trap area under the sink.

As bacteria colonies expand, they produce hydrogen sulfide gas - which emits that unmistakable rotten egg waft. Partial clogs with biofilm buildup can also block just enough flow for sulfur gases to squeeze through.

Unclogging a Smelly Drain

Getting rid of debris and gunk is key to banishing drain bacteria and eliminating foul odors. Here are some handy DIY methods to unclog that pesky pipe:

• Try a baking soda and vinegar treatment first to break up grease and food clogs.
• Use a zip-it style drain cleaning tool to hook and remove tangled hair and debris.
• Check the curved P-trap pipes under the sink for obstructions you can manually remove.
• For tougher sink clogs, use a chemical drain cleaner or call a plumber to safely snake the drain.

Reason 2: Dry or Cracked P-Trap

The U-shaped P-trap under your sink holds water that blocks methane gas and odors from the sewer lines below. But over time, that water seal can dry up if the sink drain isn't used regularly. Cracks in the P-trap can also cause water loss.

As soon as that water barrier disappears, the floodgates open for sewer gases to flow upwards into your kitchen. Even with an unclogged drain, a waterless P-trap will stink up your home.

Refilling the P-Trap

Getting clean water back in is your first step toward P-trap odor relief:

• Run hot water down the drain for a few minutes to fill up the trap.
• Check the horizontal and vertical P-trap pipes under the sink carefully for cracks that cause water leakage. Replace cracked sections as needed.
• For lesser-used sinks, install an automatic P-trap primer device to periodically reseal the water barrier.

Reason 3: Backflow of Sewer Gas from Plumbing Vents

Sewer gas smells don't always originate directly from your sink drain. Your home's main plumbing vents, designed to equalize wastewater pressure, can also allow foul odors inside.

Vent pipe issues like cracks, blockages, or improper connections can lead to methane gas backflow. Sewer vent pipes may also overflow with gases under negative pressure conditions.

Pinpointing leaky plumbing vents requires professional help:

• Have vent pipes inspected and repaired for damage cracks or gaps.
• Ensure vents aren't obstructed by nesting insects, birds, or other debris.
• Install positive pressure air admittance valves near sink drains as an extra sewer gas barrier.

Proactive maintenance is vital, but even well-maintained plumbing may see an occasional rotten egg burp from sink drains. By understanding the science behind stinky sink syndrome, you can target fixes and prevent repeat outbreaks.