It looks like a short section of bicycle tire inner tube tied off tightly at one end with nylon (?) string and tied more loosely at the other end with the same kind of string and some kind of hose adapter attached to it. What could such a thing be used for?
Hmmm… blow out a sprinkler system?
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DIY soaker hose. The thing closes off the end, punch holes in hose.
Or is that what you meant, enipla?
Nope. Many in-ground automatic sprinkler systems pipe lines are blown out with compressed air before winter so the lines don’t freeze.
I used to work for, and later owned a sprinkler system company. We worked on all kinds of systems, old and new. Sometimes you would have to come up with weird contraptions to do this.
I wonder if someone was trying to blow up 2 liter soda bottles. My first thought was that it was for launching them, but I don’t see any way to release them if you screw it into the bottle.
Are there any standard/non-weird contraptions that do this that we can compare it to?
I live where that’s not a problem so it was something I wasn’t aware needed doing.
*checks off “Learned something new today” * 
I would use such a thing to make my own pressurized squirt gun. Fill it with water from a hose until it swells, then open the valve (somehow?) and squirt your neighbor.
I think blowing out hose lines is probably more accurate, but not as fun
It’s been over 20 years, so I can’t think of any. Systems/designs change. Anyway, a properly designed newer system doesn’t have to worry about this.
I know one thing that was sort of a universal adaptor was a simple rubber toilet bowl plunger with a hole in it.
To blow out coiled garden hoses that may freeze during winter. Do not need a special nozzle on the air compressor. ???
It looks like a water pouch / waterskin / water bladder Waterskin - Wikipedia from an impoverished / developing nation with hot/dry weather.
Thanks, but I happen to know that it was found among other gardening items in a Baltic country, one of the better-off developing nations with weather that is hardly hot or dry.
My sister lives there, and was worried that it might be some kind of smoking apparatus fashioned by one of her teenaged sons. They were away when she found it. I would not have guessed it’s intent, but in this country, what the posters upthread suggested is exactly the kind of thing that resourceful people there might put together.
No confirmation yet on what it actually is intended to do (men of the house are still away), but I did convey the Dopers’ speculations (and the fact that if it was a smoking device one needs merely to sniff it), and this was enough to relieve suspicions.
Like you said, if it was used to smoke something it would smell bad and be sticky if had been used more then a few times. Besides, it would collapse when you tried to inhale since it’s not rigid.
I agree with the Its used to adapt the air pressure from the auto/bike pump ( common item ) to the hose at the end. Apart from clearing water from pipes, it could ALSO be used for anything such as inflating mattresses, toys, boats…
It sort of reminds me of those inflatable door spreaders from vehicle lockout kits.
First thing I thought of. I’ve made better…
I use my old inner tubes to stretch over wheelbarrow, shovel and tool handles that tend to give splinters every time you touch them. I’ve also rigged up something like in the picture to use as a pipe expander (damn thin walled pipe, more like a duct). Didn’t work very well. Had no way to control the airflow in the direction I wanted. But I learned something new that day.