Where the three waste pipes meet in the guttering (upstairs flat), there is like a box section. In the last couple of months, when the bath is emptied, the water comes out of the pipe so fast it hits the side of the box and cascades out and down our wall. The pipes cannot be moved so is it possible to put higher sides on the box, buy a bigger box or place something on the end of the pipes to slow the water down? The guttering is plastic.