Buy 5 litres of Isopropanol for about £10-£15 and add a can of coke full per 500ltrs,the water will bubble up on the glass as if it has detergent in it when the bubbling stops add some more.If you don`t run the tank dry you will get longer out of it,i find out of the above measure i get about 2000ltrs of working water with it.The first thing to freeze in the winter is the Y peice on the brush and the jets,Iso stops this as soon as you add it to your water.