I've just had my washing machine moved into a recently built utility area, however ever time the washing machine is emptied I end up with water all over the floor. The hose from the back of the machine is slotted into a down pipe which leads into a U bend & then horizontal pipes that run behind some kitchen units. The plumber has had a look and says there is no blockage so can't understand why the water comes back up the down pipe. Does anyone have a clue?