Since rats have been perching on the bucket rim to take soaking grains, I thought I'd have a go at making a bucket trap.
I've made a few in the past following internet directions, but none has worked. Rats are more than anything else creatures of habit, and the sudden appearance of an oil-smeared bottle sitting above a water-filled bucket makes them wary. I suspect these traps only work when there are so many rats around the place that some (particularly young ones) are absolutely desperate for food.
Last night I filled the soaking bucket so the water sat about 7.5 inches or 19cm from the top. Then I sprinkled a layer of sunflower seeds to float on top.
This morning I collected 3 large dead rats from the water. About a third the sunflower seeds had been eaten, so perhaps the seeds were a little too close to the top (some have probably eaten their fill and gotten away), but still, it's a good result.
I doubt this will work for long if I keep setting the trap in the same way. However every few nights I'll make sure the grain is right at the top of the bucket so any remaining rats can obtain a feed. Meanwhile of course I'm removing all other food sources before nightfall.
Hope this works for others as well!