"Dusty Zebra" by Clifford D. Simak. First published in Galaxy Science Fiction, September 1954, which is available at the Internet Archive; reprinted a number of times. Any of these covers look familiar?
t's a story about a device that someone found that removes dust and dirt from wherever it's placed.
He got it by trading stuff with someone in another dimension. He tests it:
The living room was spotless from Bill just having walked through it, carrying the gadget, and the garage, where he had taken it momentarily, was spic and span. While we didn't check it, I imagine that an area paralleling the path he had taken from the front door to the garage was the only place outdoors that didn't have a speck of dust upon it.
The guy who finds it shares the secret with a friend and they take it apart or somehow figure out how to replicate it with the intent of selling the objects.
No, they open one up, but they can't replicate it:
He had taken one of the dust collectors apart and the only thing he could find out about it was that there was some feeble force-field operating inside of it—feeble yet strong enough to play hell with the electrical circuits and fancy metering machinery he has at the lab. As soon as he found out what was happening, he slapped the cover back on as quick as he could and then everything was all right. The cover was a shield against the force-field.
Instead, they get a supply of the dust collectors from the interdimensional Trader, in exchange for "zebras":
It took ten days to get that shipment of fifty thousand zebras and I sweated out every minute of it. Then there was the job of getting them under cover when it came and, in case you don't know, fifty thousand zebras, even when they're only bracelet charms, take up room.
But first I took out twenty-five hundred and sent them through the desk.
One of the guys wonders where the dust and dirt go, and the other says not to worry about it.
"You know, Joe, I've been doing a lot of worrying."
"We haven't a thing to worry about now," I said, "except getting these things sold."
"But the dust must go somewhere," he fretted.
"The dust?"
"Sure, the dust these things collect. Remember we picked up an entire pile of cement dust? What I want to know is where it all went. The gadget itself isn't big enough to hold it. It isn't big enough to hold even a week's collection of dust from the average house. That's what worries me—where does it go?"
"I don't care where. It goes, doesn't it?"
They make a killing on the market and the cleaners sell like hotcakes...
But in a couple of months' time, things were running pretty smoothly. We had the state well covered and were branching out into others. I had ordered another fifty thousand zebras and told them to expect re-orders—and the desk top was a busy place. It got to a point, finally, where I had to hire three men full time, paying them plenty not to talk, to man that desk top twenty-four hours a day. We'd send through zebras for eight hours, then take away dust collectors for eight hours, then feed through zebras for another eight.
until one day the phones start ringing off the wall. Seems the original (unknown) designers didn't like all that dust and dirt flowing to their world, so they found a way to reverse the flow.
"It's the creatures from the third dimension," he said anxiously. "The place where we were sending all the dust. They got sick and tired of having it pour in on them and they got it figured out and now they're firing the dust right back at us."
