The short answer
When the basement floor drain backs up as the washing machine drains, the water has nowhere else to go. Either the line the washer drains into is clogged, usually with lint, or the main sewer line is partly clogged and the floor drain is the lowest opening in the house, so it overflows first. In Northern Virginia basements it’s almost always one of those two. Ten minutes and an upstairs tub tell you which.
Why the floor drain shows it first
A washing machine doesn’t drain like a sink. Its pump pushes out a whole tub of water in a minute or two. A drain line with a partial clog can keep up with a sink’s trickle, but not that rush. The water backs up and comes out at the lowest opening on the line, and in most houses with a basement, that’s the floor drain.
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The ten minute test
- Don’t run the washer. Mop up and let the floor drain empty.
- Upstairs, fill a tub a few inches and pull the plug, or flush a toilet three or four times in a row.
- Have someone watch the floor drain while the water runs.
- Water comes up with the washer off: it’s the main line. Stop using water and read main sewer line clog for what to do next.
- Only the washer does it: the clog is in the laundry line or the floor drain itself, most likely lint.
- It only happens in a hard rain: that points to groundwater, not the washer, and it’s worth telling us about.
If the water that comes up is gray, dark or smells like sewage, treat it as the main line either way.
If it’s lint
Washers send out lint, hair, sand and bits of fabric with every load, and in a lot of basements the washer hose drains into a laundry sink or a standpipe that ties into the floor drain line. Over years that lint mats into a plug, with soap scum holding it together.
- Pull the floor drain grate and clear what you can reach, with gloves on. Many floor drains have a trap right under the grate that fills with grit.
- Run a hand snake down the floor drain or the standpipe. How to use a drain snake.
- If the washer hose drains into a laundry sink, put a mesh lint trap on the end of the hose. They cost a few dollars, catch more than you’d guess, and you swap them when they fill.
- Skip chemical drain cleaner. It pools in a floor drain, does little to lint, and it’s still sitting there when someone reaches in. Is Drano bad for your pipes?
If a hand snake doesn’t clear it, clearing a laundry or floor drain line is $200 to $800. Our $99 sink clearing covers a sink up to the P-trap, so a laundry sink clogged at its own trap fits that.
If it’s the main line
A main line that backs up only when the washer runs is a partial clog, and partial clogs get worse. Roots in a joint, a grease plug, a belly or a wad of wipes leave just enough room for normal use, and the washer’s rush finds the limit. Clearing the main line runs $550 to $1,650. A camera down the line, $89 added to the visit, tells you why it happened, so it doesn’t happen again.
The usual causes in older Northern Virginia houses: tree roots in the line, a belly where the pipe sagged, and old cast iron scaled up inside. If grease or roots keep coming back, hydro jetting cleans the pipe wall, and hydro jetting vs snaking explains when it’s worth it.
If it already came up dirty
If the water on the floor is gray, dark or smells like sewage, keep people and pets out of it, don’t run any water, and treat it as a sewer backup. Sewer backup in the basement covers the cleanup and what to do first. A floor drain that bubbles or comes up is one of the house’s warning lights, and error codes and warning lights at home covers the rest of them.
When you’d rather we do it
A sink clogged at the trap is $99 with our sink clearing offer, up to the P-trap. A toilet, tub, shower or any drain past the trap is drain cleaning, $200 to $800. The main line to the street runs $550 to $1,650, and when grease or roots keep coming back, hydro jetting clears the pipe wall. You get the price before we start. A plumbing diagnosis visit is $49, or $250 after hours.
Call (703) 997-9757, day or night, or see every current deal on our offers page. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
Why does my basement floor drain back up when the washer drains?
Either the laundry line is clogged, usually with lint, or the main sewer line is partly clogged and the floor drain is the lowest opening, so it overflows first.
How do I tell if it’s the main line or the laundry line?
With the washer off, drain a tub or flush a toilet a few times upstairs. If the floor drain comes up, it’s the main line. If only the washer does it, it’s the laundry line.
Can I use Drano on a basement floor drain?
We’d skip it. It pools in the floor drain, does little to lint, and it’s still there when someone reaches in.
Should I keep doing laundry if the floor drain backs up?
No. Every load pushes more water into the clog and can turn a partial clog into a backup.
What does it cost to fix a floor drain backup?
Clearing a laundry or floor drain line runs $200 to $800, and the main line runs $550 to $1,650. A camera is $89 added to the visit.
