Sample Case
Option 1: Fix it yourself
Best for: a loose pipe joint or an aging seal
Turn off the hot and cold shut-off valves under the sink. Run the faucet to confirm the water is off.
Put a bucket under the P-trap and loosen the two large plastic nuts by hand. Expect a cup or two of water.
Slide the trap off. A cracked or flattened washer on a joint is the usual cause.
Match the washer (1-1/2 in is common for kitchen sinks). Reassemble hand-tight, then a quarter-turn with pliers. More than that can crack the nut.
Turn the water on, run the faucet for two minutes, and wipe each joint with a dry paper towel.