Our downstairs loo is the most used loo in our house but only for number 1’s. Seems a shame to use a full flush just for wee wee's! In my quest to conserve water and as we’ve just gone onto a meter, is it possible to convert this single flush to a dual flush? If so can I just get a replacement siphon and control button and snap it on to the existing fittings or will I have to remove the cistern to fit the replacement? Any suggestions/links for the part I want?