You don't want to get them out into nature, as they are awful pests. Some aquarists think they're good because they tunnel through the sand, but they also live and die down there, and can be a contributor to pollution in a tank. To me, they have no positives.
Killing them is not pleasant, but they would be better in compost than in a pond where they could conceivably become an environmental pest. Putting non native species outside, even if you think you can control them is always a danger.