Start at a high-volume, low-risk valve
To flush out debris, you need a high-volume flow of water. That makes outdoor hose bibs and washing machine supply lines great for this purpose. These faucets have another advantage too: Unlike kitchen or bath fixtures, they have big, simple ports that are less likely to get plugged or damaged by sediment. Just keep in mind that any faucet you choose for flushing should be downstream from the work area. Watch out! Washing machine hoses often have screens that can become plugged. Luckily, they’re easy to remove and clean. When flushing lines, you’ll be tempted to shut off the water after 10 seconds. That’s not long enough. One minute is the minimum. In a large house with long runs of supply pipe, let it flow for several minutes. Better to waste some water than to repair plugged faucets.