I installed a waterbutt last year which collects water from a garden office. But the water stinks. If I open the butt lid, I see horrible slimy stuff that looks like half-decomposed dead slug. But I don't know what it is.
I carefully emptied the waterbutt, cleaned it out etc, and it has refilled over the last week of rain. And the stink is back too.
What is causing this? and what can I do to stop it?