As a reminder, be sure to properly give content warnings and put sensitive subjects behind proper spoiler tags. It's for the mental health of not just your comrades, but yourself as well.
Here is a screenshot of where to find the spoiler button.
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What kind of waistband is it? Is it elastic?
Elastic yeah :)
You can tighten elastic waistbands by seamripping the waistband open, cutting the elastic inside so that it fits you, and then sewing the waistband back up. Kind of like this. Handsewing works perfectly well for this. I tightened a pair of pants with an elastic waistband and honestly it doesn't look perfect, but I'm okay with that because I doubt anyone is inspecting waistbands when they meet people.
Very fair. Safety pins are always there for these situations