I'm having a new toilet fitted in my bathroom and the plumber has told me that he can't fit it right against the wall, I think due to the angle of the waste pipe. The pipe comes in through the external wall and then has to turn 90 degrees to go into the toilet. The plumber has suggested building a "box" at the back of the toilet to conceal the gap and the waste pipe below, so I'll effectively have a shelf behind the toilet. Is there really no other way round this problem?