Whether you’re dealing with a clogged toilet or want to make sure your water heater is working properly, having some basic home plumbing skills can help. And while most people panic at the sight of a jumbled diagram with arrows going every which way, your home plumbing system actually follows quite logically from simple laws of nature like gravity and water seeking its own level.

Your home’s home plumbing system has two subsystems — the supply system that delivers freshwater and the drainage system that removes wastewater. Each system works independently of the other, but both rely on a series of pipes to function.

Water enters your home through a main supply line, which connects to your water heater before splitting into cold and hot water supply lines. Most homes also have a shutoff valve where the water meter is located, which allows you to turn off all water to your house in case of emergency (or just to save money on your water bill).

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All fixtures like sinks, tubs, toilets and even appliances like dishwashers and washing machines have drains, which are designed to keep waste and freshwater separate. All drains, however, must be kept clear of food scraps and cooking fat, which can cause a buildup that leads to a blockage or stinky sewer backup.

To prevent this, all drains have traps – u-shaped sections of pipe at the back of each fixture that hold a little water to ensure nothing goes down the drains besides water and waste. Traps are especially important for your kitchen, where you should be careful not to put grease down the drain.