The 5 causes ranked by field frequency
| # | Cause | Field frequency | Fix |
|---|---|---|---|
| 1 | First-gen 1.6 GPF low-flow toilet (1994-2005) | ~35% | Replace with modern 1.28 GPF MaP ≥800 |
| 2 | "Flushable" wipes accumulating in lateral | ~25% | Stop using them; auger or camera the lateral |
| 3 | Mineral buildup in trapway (hard water, 20+ year-old toilet) | ~15% | Vinegar soak under rim + bowl; replace if extensive |
| 4 | Partial main-line blockage | ~15% | Camera + auger from cleanout |
| 5 | Vent stack issue (weak siphon) | ~10% | Clear roof vent — see drain gurgling diagnosis |
The MaP rating — the spec nobody talks about
MaP (Maximum Performance) is the industry test that measures how many grams of solid waste a toilet can flush in a single 1.28 GPF cycle. The MaP scale runs 0-1,000 grams. Higher is better. WaterSense-certified toilets must hit MaP ≥350. The best modern toilets hit MaP 1,000 — flushes nearly anything you'd reasonably put in it.
If your toilet is 1994-2005 first-gen 1.6 GPF: it likely tests at MaP 200-400. Modern 1.28 GPF TOTO Drake, Kohler Cimarron, or American Standard Champion 4 test at MaP 800-1,000. Modern low-flow flushes BETTER than old high-flow. Engineering has improved dramatically. A $300 replacement toilet beats $150 service calls every two months.
The "flushable wipes" reality
INDA (Association of Nonwoven Fabrics Industry) tests confirm "flushable" wipes don't break down like toilet paper. They survive the flush, collect at bends in the lateral line, then catch other debris. Wipes are the #1 cause of recurring partial clogs in homes built after 2015. Major US cities (NYC, DC, Vancouver BC) have sued wipe manufacturers over sewer-system damage. Per IAPMO plumbing code, only material approved for sanitary sewer is toilet paper. Stop using wipes.
DIY diagnostic flow
- Single clog, easily plunged? Probably user error. Moving on.
- Clogs every 1-2 weeks? Suspect first-gen 1.6 GPF toilet. Check the date stamp inside the tank (top of fill valve or back of bowl). 1994-2005 = replace.
- Multiple drains slow at the same time? Main-line partial blockage. Camera + auger needed.
- One toilet, no other drain affected? Localized — either toilet design, mineral buildup in this trapway, or wipe accumulation in the short lateral run from this toilet.
- Gurgling drain in nearby sink when toilet flushes? See vent stack diagnosis — weak siphon is the cause.
FAQ
Why does my toilet keep clogging?
5 causes: first-gen low-flow weak siphon, "flushable" wipes, mineral buildup, partial main-line blockage, vent stack issue. Replace if it's a 1994-2005 1.6 GPF unit.
Are flushable wipes really flushable?
No. They don't break down. #1 cause of recurring clogs post-2015. Stop using them.
Will an auger fix recurring clogs?
Augering clears a current clog but doesn't prevent the next. Clogs every 2-3 weeks = deeper problem.
Should I replace a constantly-clogging toilet?
Yes if 1994-2005 first-gen 1.6 GPF. Modern 1.28 GPF MaP ≥800 flushes BETTER. $200-$400 installed beats $150 service calls.
Related guides
- Toilet keeps running — different problem, often confused with clogging
- Drain gurgling sound — vent stack diagnostic
- Best plumbing inspection cameras 2026 — for finding main-line partial blockages
Editorial standards: Cited authorities include MaP (Maximum Performance) toilet flush testing protocol, EPA WaterSense certification (MaP ≥350), IAPMO Uniform Plumbing Code, INDA flushable-wipes testing. Reviewed by Al, Building Doctor — IUOE Local 39 Stationary Engineer.