On Friday, September 16, 2016 at 10:25:45 AM UTC+1, Muddymike wrote:
I have a plastic dustbin in use as a water butt one side of my
greenhouse. I lift the lid and dunk the watering can to fill it.

I often find slugs around the inside of the bin rim and knock them into
the water. They always sink towards the bottom but more appear quite
regularly, hence my question.

Mike

Yes I did the same in an enclosed water butt, knocked bit fat slug off above the water line he spiralled to the bottom but was back the following morning!