Run the dye drop the same way every time

Lift the tank lid. Add several drops of dark food coloring or a dye tablet to the tank only. Do not flush. Start a timer. Any color in the bowl without flushing means tank water is crossing the flapper or flush-valve seat.

Classify Slow seep vs Fast waste

Use the clock, not the sound:

• Color in under ~5 minutes → Fast waste (often tens to ~200 gallons/day).
• Color around 5–15 minutes → Slow seep (still bill-moving over a full cycle).
• No color after 15 minutes → tank-to-bowl path likely sealed — keep screening with a meter test.

Confirm on the meter if the house is quiet

A positive dye test is enough to fix the flapper. Pair it with a quiet-house meter check when you want gallons/day proof for a utility conversation or to catch non-toilet flow.

Translate the leak into bill language

If the dye failed and the bill spiked, size dollars with the silent-leak cost path — sewer often bills the same gallons again. If the dye passed but the bill is still high, branch to rates, outdoor use, or a high-bill review.

When dye passes but the bill still jumped

Clean dye tests do not clear irrigation, tier jumps, estimated true-ups, or guests. Use the no-leak branch before replacing fixtures.

Document for a leak adjustment if your utility offers one

Photo the colored bowl, note the repair (flapper brand/size), and keep before/after meter readings. Policies vary — volume drop on the next cycle is the strongest proof.

Fix vs replace after the path is sealed

Most silent leaks are a $5–$20 flapper, not a new toilet. Re-dye after the fix. Only then evaluate a WaterSense replacement for long-term efficiency.