No smell or mess with that method according to the instructions on the box if you don't have a problem with drowning them. Many millers think that you would not have to provide the cat with a litter box if it has access to the outside. Even mill cats need litter boxes in the mill or they will find an area in the mill that they will used as a litter box. A cat in a mill needs to be treated just like a house cat and be taken to the veterinarian regularly for shots and a checkup. This may add to the contamination of the building and the grain by rodents.
Cats seem to like to use buckwheat seeds as cat litter.
Perhaps it is because of the hulls of the buckwheat are used to cover up human scents by hunters when setting traps. I have also tried to grow buckwheat sprouts around my mill cat and as soon as it sprouts into leaves they will eat it down to the dirt. There is nothing like the partnership that develops between a miller and his cat. I can't help it when someone mentions a miller cat not to think about the late Charles Howell's mill cat. Dusty would run along the hand-railing of the bridge over the mill dam next to the Philipsburg Mill as Charlie walked over the bridge.