Discoloured spots found around your toilet is mineral build-up, which, over time, stains the seat if not quickly and effectively cleaned with a neutralising cleaning agent. Yellow stains require a special hydrochloric-based cleaner to break up the stain and lighten the spot. Hydrochloric cleaners that are suitable for your toilet include in-bowl toilet cleaners meant to clean the inside of toilet bowl. According to "Good Housekeeping The Complete Household Handbook" a well-ventilated area is required while cleaning the bathroom with chemical-laden products to avoid inhalation.
Open a window or turn on your bathroom's ventilation fan to reduce chemical exposure.
Place the protective mask over your nose and mouth and put on the rubber gloves.
Pour the cleaning product directly onto the toilet seat's stain and allow it sit on the stain for 10 minutes to break up the mineral deposit. Leave the room while the cleaning product is on the toilet seat to minimise exposure.
Scrub the spot in a circular motion to break up the stain.
Wipe the area with a clean, damp cloth and dispose of the cleaning cloth immediately after using it.
Leave the bathroom fan or window open for two to three hours after cleaning until the product's smell dissipates from the bathroom.
Do not use an abrasive cleaning product as it can easily damage the toilet seat's finish, according to the official Kohler site. Do not mix chlorine bleach with the hydrochloric cleaner as it creates chlorine gas that irritates the lungs and causes breathing problems, according to The New Jersey Department of Health and Senior Services.