Short definition
Rim holes (or rim jets) are the small diagonal holes drilled around the underside of a toilet bowl rim. They direct flush water in a swirling, spiraling pattern around the bowl interior — what makes a flush actually scour the bowl rather than just dropping water down the trapway. Typical residential bowls have 8 to 24 rim holes.
What it is
Each hole is angled to spiral water clockwise around the bowl (in most North American toilets). The siphon jet — a single larger hole at the bottom of the bowl — drives the actual flush; the rim holes scour the porcelain on the way down. Together they produce the visible swirl and the post-flush clean bowl.
When rim holes scale shut from hard water or get blocked by bacteria slime, the flush goes weak and uneven — water spirals on one side, runs down the back, or skips parts of the bowl entirely.
Why it matters to a homeowner
The clean-bowl part of the flush depends on rim holes working. If your toilet “doesn’t flush as well as it used to” without any tank or fill changes, the rim holes are the most likely culprit — especially in Spokane and other hard-water areas where mineral scale plugs them over years.
Cleaning options:
- Mineral scale. Vinegar or commercial descaler (CLR, Lime-A-Way), with the water shut off and bowl drained. See mineral-clogged-rim-holes.
- Bacteria slime / mold. Bleach with a wire pick. Different chemistry, different cleaner.
- Both can co-occur. Clean for both before declaring the bowl is “weak by design.”
If you’re shopping for a new toilet in a hard-water area, look at rimless bowl designs — a single jet at the front of the rim eliminates the small holes and the cleaning chore.
Common variants and what it isn’t
- Rim holes (this entry) vs. siphon jet. Rim holes scour the bowl. Siphon jet drives the flush.
- Rim holes vs. rimless bowl. Modern flush design with a single jet at the front of the rim instead of distributed small holes.