The answer to 'when to replace drain trap' is that you should replace your drain trap if it is cracked, corroded, or leaking. The drain trap is the curved pipe under your sink that helps prevent sewer gases from entering your home. Over time, the trap can become damaged and need to be replaced to maintain proper drainage and prevent odors.
Drain traps typically last 5-10 years, but the lifespan can vary depending on the material (plastic vs. metal) and the water quality in your home. Signs it's time to replace the trap include slow draining, standing water, and visible cracks or corrosion. Replacing the drain trap is a relatively simple DIY project, but if you're not comfortable doing it yourself, it's best to hire a professional plumber.