I used this for chipmunks ( cutest rodents on earth) - they were nesting in the crawl space under my kitchen - what a disaster.5 gallon bucket... use small can, soda can, whatever, put small holes with nail in each end as close to centered as you can... string heavy duty wire through it and secure to top of bucket... push can down in center to bend wire on either side of can to keep it centered on wire... smear peanut butter, rodent attractant around can... make ramp or some kind of access for rats to get to top edge of bucket... put a few inches of water in bucket (I top with veggie oil for good measure) and rats will put front feet on can to get the bait, can spins and causes rats to fall in bucket and drown...
These rats can jump high, so I added oil to help keep them from getting out... or use a 30 or 55 gal drum...