Gtechniq W4 Citrus Foam 1 Liter | Pre-Wash Snow Foam 1000ml | The Clean Garage. Why use W4 Citrus Foam?. For best results use in a snow foam lance, out of direct sunlight. It can be used at a dilution of up to 1:400 through a foam lance, or up to 1:25 through a pump sprayer.