The laws and regulations regarding plumbing work without a license vary by location and jurisdiction. In general, it is illegal to perform plumbing work without a license in most areas. However, there may be some exceptions for small, simple jobs that homeowners can do themselves. These may include:

Unclogging a drain: You can use a plunger or a drain snake to unclog a drain.

Replacing a simple faucet washer: You can replace a simple washer on a faucet by turning off the water supply to the faucet and replacing the washer.

Installing a new toilet: You can install a new toilet, as long as you’re not modifying the existing plumbing and you’re not relocating the toilet.

Replacing a toilet flapper: You can replace a toilet flapper if it is worn or leaking.

Changing an air filter: You can change the air filter in your HVAC system.

It’s important to remember that even when you’re doing work that may not require a license, you should still comply with all local building codes and regulations. And even if a task is considered as small and simple, if you’re not comfortable with it or if you’re not familiar with plumbing, it’s best to call a licensed plumber to do the job, as it’s important to have a proper installation and to avoid any leaks or damages.