Start at the bottom. Pull off the bottom elbow and clean it out, then run a garden hose down from the top, and only reach for a plumber's snake if the hose won't push the clog through. That's how to unclog a downspout in most cases, and the first step usually happens from the ground.
Here's the whole job, in order.
How you know it's the downspout
Watch the gutter during a hard rain. If water spills over the front edge right above a downspout while only a trickle comes out the bottom, the downspout is clogged. If water spills over in the middle of a long run instead, the gutter itself may be full or sagging, and that's a different fix. Our post on when to clean gutters covers that side of it.
What you'll need
- Work gloves
- A screwdriver or a drill, for the screws that hold the elbow
- A garden hose with a spray nozzle
- A plumber's snake, the hand-crank kind
- A sturdy ladder and somebody to hold it, if you have to reach the top
- A bucket or an old tarp for the muck
Step by step
- Pull the bottom elbow. It's usually held by a couple of small screws, or just pushed onto the end of the pipe. A lot of clogs sit right here, where the water has to turn.
- Clean out the elbow by hand, or flush it with the hose. If you pulled out a solid plug of leaves, run water from the top before you put the elbow back on.
- Clear the gutter around the top of the downspout. From the ladder, scoop the leaves away from the hole where the gutter drains into the pipe.
- Run the hose down from the top. Feed it into the downspout from the gutter and turn it on full. If water runs freely out the bottom, you're done.
- If it backs up, use the snake. Feed it in from the bottom first, since that end is easier to reach, and crank until you feel the clog give. Then flush again from the top.
- Tap the side of the pipe while the water runs. On a stubborn clog, that can shake it loose. Don't hammer on it, because thin downspouts dent.
- Put it back together. Screw the elbow back on and make sure the extension at the bottom sends water away from the house, not toward the foundation.
Downspouts that run underground
Some houses tie their downspouts into a buried pipe that runs out to the yard or the curb. Those clog too, and they're harder to see.
The signs are water bubbling out at the joint where the downspout meets the ground pipe, a strip of lawn that stays soggy along the run, or nothing at all coming out the far end. To check, disconnect the downspout at the joint and run the hose straight into the buried pipe. If it backs up, run the snake in from that end.
If a car crushed the pipe or roots grew into it, no snake will fix that, and somebody has to dig. If you're buying a house, know that InterNACHI's home inspection standards say the home inspector isn't required to inspect underground downspout drain pipes. Ask the seller where those pipes come out.
When to call someone
Call for help if reaching the top means standing on a ladder at a two-story roofline, if the same downspout clogs again a few weeks later, or if the gutter is pulling away from the fascia. A clog that keeps coming back usually means the downspout is too small for the roof above it, or the trees overhead are winning.
Our opinion: if a downspout clogs more than once a year, a better snake won't solve it. A guard over the gutter outlet will, or a larger downspout, or both. See gutter guards for what holds up under which trees, and the gutters page if yours need replacing.
Questions
Can I use a pressure washer to clear a downspout?
We wouldn't. It can knock the elbow joints apart and send water where it shouldn't go. A garden hose with a strong nozzle does the job.
How often should downspouts be cleaned?
Whenever the gutters are. Under heavy trees, that can mean a few times a year.
