Shower Drain Smells: Causes, Fixes and How to Prevent It

Sep 20, 2026

A foul smell coming from the shower drain is one of the most common bathroom complaints - and one of the most misdiagnosed. Builders get called back for what looks like a drainage defect, when in most cases the cause is a dry trap, a blocked outlet, or a maintenance issue the homeowner can fix.

The most likely cause of a smelly shower drain is a dry P-trap. The P-trap (or S-trap) is the curved section of pipe beneath the drain that holds a small volume of water. This water acts as a seal, blocking sewer gases from rising back up through the drain into the bathroom. When a shower isn't used for a period — a guest bathroom, a holiday home, or a newly completed build waiting for handover - the water in the trap evaporates and the seal breaks.

The Four Most Common Causes

1. Dry P-Trap (Most Common)

When the water seal evaporates, sewer gas enters the bathroom through the drain. This is the cause in the majority of cases.

Fix: Run the shower for 30 seconds. This refills the trap and restores the water seal. For showers used infrequently, run water through the drain fortnightly to keep the trap wet.

2. Blocked or Partially Blocked Outlet

Hair, soap residue, and debris accumulate in the drain channel and outlet over time. A partial blockage slows drainage and creates stagnant water that breeds bacteria and biofilm.

Fix: Lift the grate, clear the drain channel of debris, and flush the outlet with clean water. For deeper blockages, use a plumber's snake or drain-clearing solution.

3. Biofilm Buildup

A slimy bacterial film builds up on the inside of drain channels and pipes. It feeds on soap, body oils, and organic matter. The smell is the bacteria breaking down this organic material.

Fix: Remove the grate, clean the drain channel with a non-abrasive cleaner, and flush thoroughly. For stainless steel drains, a mild detergent and warm water is sufficient - avoid abrasive chemicals that damage the finish.

4. Plumbing Vent Issue

If the drain smells despite a full trap and clean channel, the plumbing vent may be blocked or incorrectly installed. A blocked vent creates negative pressure that siphons the trap water, breaking the seal.

Fix: This requires a licensed plumber. The vent stack (typically on the roof) needs inspection and clearing.

When Is It the Drain's Fault?

In rare cases, the drain itself contributes to the problem:

A cracked or poorly sealed drain body can allow sewer gas to bypass the trap entirely
A drain installed without adequate fall creates standing water in the channel
A damaged or corroded outlet connection loses the watertight seal

If cleaning and trap maintenance don't resolve the smell, the installation should be inspected by a licensed plumber.

Prevention

Action	Frequency
Run water through infrequently used drains	Fortnightly
Clean grate and drain channel	Monthly
Flush outlet with clean water	Monthly
Full drain clean (remove grate, scrub channel)	Quarterly

Frequently Asked Questions

Q: Why does my new shower drain smell?

Most likely a dry P-trap. New builds sit unoccupied during the final stages. The trap water evaporates, breaking the gas seal. Run the shower for 30 seconds and the smell should resolve immediately.

Q: Can I pour bleach down the drain?

Use with caution. A mild solution can help kill bacteria, but harsh chemicals can damage stainless steel finishes and pipe seals over time. Warm water and mild detergent is preferred for stainless steel drains.

Q: Do I need to replace the drain if it smells?

Usually not. In 90% of cases, the cause is maintenance-related (dry trap, debris, biofilm). If the drain body is cracked, corroded, or poorly sealed, replacement may be warranted.

Q: Where can I get replacement shower drains?

Vincent Buda and Company stocks linear shower drains in all common sizes and patterns — same day dispatch for Sydney Metro orders before 12 pm AEDT, or next day delivery Australia-wide.