[Translate to Ukraine / Україна:] Dense sintered sanitary porcelain is one of the easiest materials to maintain. And if you choose porcelain with a Ceramicplus surface treatment, then it is even easier to keep clean.
Clean the porcelain often to prevent dirt and limescale deposits forming. If your regular detergent does not give the desired result, try citric acid or tartaric acid. Dilute according to the manufacturer's instructions and apply to the WC bowl. Wipe/rub the damp surface dry and rinse thoroughly. Remove limescale deposits with household vinegar. Dilute according to the manufacturer's instructions. Heating the vinegar will provide an even better result.
Never use abrasive detergents. They damage the glaze over time. And never use strongly alkaline, lye-based blockage removers that can damage the porcelain surface and harm the environment.
For toilet bowls stored in unheated areas, the cistern should be emptied and wiped dry. Pour about 4 dl (14 fl. oz.) of antifreeze in the water trap. Use an environmentally-friendly product.