First, gather all the necessary tools and materials. Place an old towel or a small bucket on the floor directly below the toilet's water supply line connection to the shut-off valve and the toilet tank. This will protect your floor and catch any water that drips out during the replacement process. Ensure your work area is well-lit and clear of obstructions.

Locate the water shut-off valve, typically an oval-handled valve on the wall or floor behind the toilet. Turn the handle clockwise until it stops to shut off the water supply. Do not force it. Next, flush the toilet and hold the flush handle down to drain as much water as possible from the tank. Use a sponge or towel to soak up the remaining inch or so of water from the bottom of the tank.

With your bucket and towel in place, start by unscrewing the coupling nut that connects the supply line to the plastic threads of the toilet's fill valve (the bottom of the tank). This is typically a plastic nut and can often be loosened by hand. If it's tight, use an adjustable wrench or pliers gently. Next, use the adjustable wrench to loosen and unscrew the nut connecting the supply line to the shut-off valve on the wall. Once both ends are disconnected, remove the old supply line.

Take your new Braided Stainless Steel Toilet Supply Line. Ensure the rubber cone washers are properly seated inside both coupling nuts. The larger nut (typically 7/8-inch ballcock) connects to the toilet fill valve, and the smaller nut (typically 3/8-inch compression) connects to the shut-off valve. Position the new line, making sure it isn't kinked or twisted, and that it reaches both connection points without being stretched.

First, thread the larger coupling nut onto the plastic threads of the toilet's fill valve. Tighten it by hand until it is snug. Be careful not to cross-thread it. Next, thread the smaller coupling nut onto the shut-off valve. Hand-tighten this nut as well. Once both are hand-tight, use your adjustable wrench to give each nut an additional quarter-turn to a half-turn. Do not overtighten, especially the plastic connection on the fill valve.

Ensure the connections are dry by wiping them with a paper towel. Slowly turn the shut-off valve handle counter-clockwise to turn the water back on. Listen for the tank to start filling. As it fills, carefully inspect both the upper and lower connections for any signs of dripping. Use a dry paper towel or your fingers to feel around the nuts for moisture. If you detect a leak, turn the water off and tighten the leaking nut slightly (about an eighth of a turn), then test again. Once the tank is full and the connections are dry, flush the toilet once to put the system under pressure and perform a final check for leaks.