Something smells in your kitchen and you cannot find it. The bin is empty, the surfaces are clean, and it is worse when the tap runs. You have poured bleach down the sink and it came back within the day.

The smell is not in the drain. It is in the grind chamber above it: the housing where the food is broken up, which has a rubber splash guard, a ring of ledges and a set of blades, and every one of those holds a film of decomposing food that water never touches on its way through. Pouring anything liquid down there is the same mistake as with a drain cleaner. It goes straight past the walls and into the pipe, where there was no problem.

A foaming tablet is built for exactly that shape. It reacts with water and expands, so it fills the chamber and reaches the underside of the splash guard, the ledges and the back of the blades. It cleans a volume rather than a path, which is the difference between treating the smell and rinsing near it.

Run the disposal briefly with a little water and then stop while the foam is still up there. The habit of running the tap hard is the one thing that undoes it.

Here is the limit. This is deodorising and cleaning, not unblocking. If your sink is draining slowly, that is a different product and a different problem, and tablets will not help.

It is also not for a smell that is coming from somewhere else. Sink drains, dishwasher filters and the trap under the basin all produce a very similar odour, and people buy this and then discover the real source. Run the disposal and see if the smell rises before assuming.

And it does not last. This is on a schedule, roughly every couple of weeks depending on what you put down there. Twenty-four tablets is about a year.