Why Does My Floor Drain Back Up When the Washing Machine Drains?
- 4 days ago
- 3 min read
When your washing machine drains, it moves a lot of water very quickly. If that water suddenly comes up through a nearby floor drain, it’s more than just gross — it’s a warning sign that something isn’t right in your plumbing system.
This is a common problem for Metro Detroit homeowners, especially in older homes with shared drain lines. Let’s break down why it happens, what it means, and when it’s time to call a professional.
What’s happening when your floor drain backs up?
Your washing machine empties into your home’s drain system at a high volume. If the main drain line can’t handle that flow, the water looks for the lowest exit point — and that’s often the basement floor drain.
Instead of flowing out to the sewer, wastewater pushes back up where it can.
Most common reasons this happens
A partial blockage in the main drain line(the most common issue we see)
Over time, your main sewer line can collect:
Lint from laundry
Soap residue
Grease and food particles
Tree roots (very common in Michigan)
If your washing machine drains into a laundry sink (utility tub) before entering the main drain line, lint may be contributing to the problem.
Even though washers have internal lint filters, they don’t catch everything. Over time, excess lint can build up inside the drain pipe, combine with soap residue and cause blockages.
A simple and inexpensive solution is installing a lint trap on the washing machine discharge hose(see image below). These mesh traps catch debris before it enters your plumbing system.
You can find lint traps at most hardware stores and online - check out the links below!
The washing machine and floor drain share the same line
In many older Metro Detroit homes, basement floor drains and laundry drains are connected.
That setup works until the pipe starts narrowing from buildup. Then, every wash cycle becomes a stress test for your plumbing.
Improper pipe slope or aging plumbing
Older cast iron or clay pipes can:
Sag over time
Corrode on the inside
Collect debris more easily
Even a small dip in the line can cause water to pool and slow drainage.
Is a floor drain backup serious?
Short answer: yes.
Even if it only happens during laundry:
It can lead to sewage backups
It increases the risk of basement flooding
It may signal a bigger sewer issue developing
Catching it early can save you from a much more expensive repair later.
What you should (and shouldn’t) do
DO:
Stop running water when you notice a backup
Keep the area clear and avoid contact with wastewater
Call a licensed plumber to inspect the drain line
DON’T:
Ignore it because “it drains eventually”
Rely on chemical drain cleaners (they rarely fix main line issues)
Keep running laundry — it can make the blockage worse
How CMC fixes floor drain backups
At CMC Plumbing, Heating & Cooling, we typically start with a camera inspection to see exactly what’s happening inside your drain line.
From there, solutions may include:
Professional drain cleaning
Hydro jetting to clear heavy buildup
Tree root removal
Sewer line repair or replacement (only if needed)
We focus on fixing the cause, not just the symptoms.
Floor drain backing up in Oakland or Macomb County?
A backing-up floor drain is one of those problems that rarely fixes itself — but it is very fixable with the right approach.
Based in Madison Heights | Serving Metro Detroit
📞 248-546-8800 | 📧 service@cmcphc.com
Disclaimer: The information provided in this blog is for general educational and informational purposes only. Every home and system is different, and not all advice may apply to your specific situation. For personalized recommendations, code-compliant work, or professional service, please contact CMC Plumbing, Heating & Cooling. We’re licensed, experienced, and happy to help you get the job done right.
