As the subject really. Is there any reason why I shouldn't pipe an overflow from the side of a cistern down and under said cistern and tee into flush pipe? If so, is there a reducing tee type fitting that would take 22mm overflow pipe into the side of 38mm flush pipe? The current overflow goes into a room soon to be a kitchen (hopefully). I want to keep the existing cistern, box it in and fit a back to wall pan. This way I have one toilet in the house that gives a decent flush volume (unlike the flush three times 6Litre models currently on the market).