Helping a friend with replacement wc. We are trying to connect pan to soil pipe in floor, but using this pipe the toilet is sitting about 7 inches away from wall. (Have used a McAlpine swan neck, but too tall) He says there is an above ground soil pipe the other side of the rear wall (behind wc) Is he allowed to knock a hole through this wall and connect to the outside waste pipe, so then the wc will sit against the wall rather than 7 inches away from it! Thanks in advance.