It's believed the person was putting their own garbage into the large bin when they heard a rustling sound, saw the snake and called police.
"A member of our canine unit did attend ... and he was able to safely contain the snake in a (smaller) recycling bin," Const. Jason Michalyshen said Wednesday.
"Not everybody feels comfortable with a situation like that, but certainly members of our canine (unit) go above and beyond what they do on a daily basis."
The serpent turned out to be a ball python — smaller than most other types at just over a metre long and not poisonous. But officials were still relieved it didn't slide out of the Dumpster.
"We're glad that it didn't get out and a child didn't come across it on the streets," said Leland Gordon, chief operating officer of the city's animal services department.
Winnipeg police dealt with a more dangerous reptile in 2008, when a man was bitten in the face by a poisonous gaboon viper that was on the loose. Antidote had to be flown in from Ontario.
On other occasions, city police have had to deal with pet snakes escaping into adjacent apartments.
An investigation is underway to find the python's owner, who could face charges under the provincial Animal Care Act. The law carries a maximum penalty of a $10,000 fine and six months in jail.
Gordon urged exotic pet owners to keep tabs on their animals and not abandon them.
"It's very important that people who own exotics understand that there's a portion of our community that is terrified of snakes, obviously. So when you have a snake like this, find a home for it if you don't want it."
The serpent was in good shape, despite spending an evening in the cool spring weather.