Siamp 'Optima 50' Dual Flush Valve 2" plus 1.5" Outlet This dual action flush valve is perfect to replace and refresh a tired old cistern, making your toilet more economical and run smoothly and trouble free!! Siamp is unanimously considered to be a worldwide leader in innovation and modern technical solutions in the sanitary market. Every product designed and manufactured by Siamp encompasses their main principles of efficiency, viability and sustainability. This is perfectly reflected in their cable operated 'Optima 50' dual flush valve (2"), which is why it is one of the most widely used dual flush valves for toilets with a plastic or ceramic cistern.