Step 6 · Install the New Cartridge
Prepare the new cartridge for installation. If it came with new O-rings, apply a very light coating of plumber's grease to them. This helps them seat without tearing and creates a better long-term seal. Align the new cartridge based on the orientation you noted from the old one (there are often tabs or notches that fit into corresponding slots in the faucet body). Carefully slide the new cartridge down into the faucet body until it is fully and firmly seated.