A rimless toilet replaces the traditional under-rim water-distribution holes (where bowl-cleaning water enters during a flush) with a single curved jet that delivers water around the bowl from the front. No under-rim space means no hidden hideout for bacteria, mineral buildup, or grime.
On a traditional toilet, the rim of the bowl has a hollow underside containing 6–12 water-distribution holes that direct flush water down into the bowl. That under-rim space is impossible to see (you have to physically lift the bowl seat and bend down) and very difficult to clean. Years of mineral buildup accumulate inside those rim holes; bacterial growth happens there. Periodically, the buildup becomes severe enough that flush water no longer flows properly through the holes, and the bowl-cleansing degrades.
A rimless design eliminates the under-rim entirely. Instead, a single curved jet at the back of the rim delivers water that spirals around the bowl via centrifugal force. The bowl interior is fully visible from above — no hidden surfaces. Cleaning a rimless bowl takes one wipe; a traditional rim toilet requires periodic deep cleaning under the rim with specialty brushes.
Rimless flush mechanisms work well but require more flow velocity than traditional rim-hole distribution. Most rimless toilets are 1.28 GPF or higher; sub-1.0 GPF rimless designs exist but are less common. The bowl-cleansing on a rimless toilet is often more effective than equivalent rim-hole design because all the flush water is contributing to the spiral rather than being split across 8–12 small holes.