OLPRO Bottom and Top is a toilet rinse additive that can be used for both top tanks and bowls. It leaves the system clean, free of bacterial and smelling fresh. Formaldehyde free, will not damage the toilet and environmentally friendly. Votedessential product by Practical Caravan for 2013 and is now our number one selling Chemical product. Directions: Add 100ml of OLPRO Bottom and Top to every 20 Litres of water.