I bought two of these from Ebay, £6.50 each. I put them on a 50L plasterers bucket, the sort with vertical straight sides. I found that the placement of the filling holes tended to get clogged with gunk, just silt, mud, grit, grass etc... Maybe in with birds who aren't free ranging it might have worked better. Not to be deterred I put them on a 300L waterbutt. Had this idea that I'd twist them upside down to clean them out, the water pressure of the large butt would clean them out. This did work better. But as with most water, it froze solid when temp dropped. Then cracked as the ice expanded inside them.
DJ Chook