Summer Pest Alert: How to Get Rid of Drain Flies and Sour Sink Smells in June

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As the June heat and humidity start to roll in, we all expect to deal with a few extra bugs outside. But there is one pesky summer visitor that nobody wants to find inside their home: drain flies.

If you’ve noticed tiny, fuzzy gnats hovering around your kitchen sink, bathroom shower, or basement drain, you’re not alone. June is prime time for these annoying pests.

Let’s look at why they show up the minute the weather warms up, and how to safely get rid of them and the sour odors they bring with them.

Why Do My Drains Smell (and Grow Bugs) in June?Drain flies don't just wander in through an open window; they are actively attracted to your plumbing.

Over months of use, a sticky layer of soap scum, grease, hair, and organic food particles builds up along the inside walls of your pipes. This coating is called biofilm. When summer temperatures rise in June, that trapped organic matter begins to decompose much faster, releasing a sour, musty odor up into your home.

To a drain fly, that rotting biofilm is paradise—it’s exactly where they lay their eggs. Within days, a minor buildup can turn into a full-blown gnat infestation.

The Wrong Way to Fix It: Boiling Water and BleachThe most common DIY "hacks" people try are pouring boiling water or straight bleach down the drain. Unfortunately, these rarely work for long:

Bleach is a great sanitizer, but it runs right past the thick, gooey biofilm without actually breaking it down. The flies living deep inside the muck will survive, and the eggs will hatch a few days later.

While hot water can help kill surface larvae, pouring boiling water down a bathroom sink or toilet can crack porcelain fixtures or soften and warp PVC pipes beneath the counter, creating hidden water leaks.

To get rid of pests, you have to eliminate their food source. Here is how to clean the line without damaging your plumbing:

1. Scrub the Drain Mechanical StyleThe best way to destroy biofilm is old-fashioned scrubbing. Remove the sink stopper or shower grate. Take a long, stiff pipe brush (or an old toothbrush) and scrub the inside walls of the pipe as far down as you can reach to physically break up the slime.

2. Use an Enzyme Drain CleanerInstead of harsh, corrosive chemicals, use an enzyme-based drain cleaner or a specialized drain gel. These products contain live bacteria cultures that naturally eat away at organic grease, hair, and soap scum over several hours. Pour it down the drain before you go to bed so it can sit undisturbed overnight.

3. Flush Inactive DrainsDo you have a guest bathroom shower, a basement floor drain, or a wet bar sink that rarely gets used? When a drain sits empty, the water inside the P-trap (the curved pipe beneath the floor) evaporates. This allows sewer gases—and bugs—to travel straight up into your living space.

Pro Tip: Every couple of weeks in the summer, run the water in your unused sinks and showers for 30 seconds to keep the traps filled and seal out odors.

Still Smelling Something Sour?If you’ve scrubbed your drains and used an enzyme cleaner, but that musty sewer smell just won't go away, the blockage might be deeper in your main sewer stack, or a vent pipe on your roof might be clogged with debris. When DIY methods don't cut it, give Tony's Plumbing & Heating in Oakdale, MN a call to perform a professional drain cleaning to restore your home’s fresh air. 

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