I very much advise you wash your sloes before freezing otherwise you might end up with a few (used to be) living hedgerow beings in your finished gin. I’m not sure anybody would appreciate you pouring them a spider.
When you go out to pick your sloes I must warn you that 1kg of sloes is a good couple of hours of work, scratched wrists, attack of the stinging nettles and excellent fun if you take a friend. I’m not making it sound very appealing but what you get at the end of all the work makes it so worthwhile. You can take a look at this handy guide if you’re new to foraging to help you identify the sloes. I also have a few golden nuggets of foraging advice too.