If your Xsara is like ours, there's no drain on the bottom of the radiator. You'll need to disconnect the bottom hose to empty the rad. Also remove the reservoir cap and open the bleed caps. There's a drain for the block on the rear lefthand side, but to get to it you'll need to remove the lower engine tray. Since I replace the coolant every two years, I just drain the radiator, flush it through, then add fresh water and antifreeze.