Hi All I'm just in the process of fitting a new bath and sink and would like to tidy up the waste pipework. At the moment the bath has a 40mm pipe going through the outside wall into a hopper and the sink has a 32mm pipe also going through the outside wall into the hopper. I'd like to join the two together but as a DIYer I'm not sure if this is against building regs or if joining the two will cause problems. I suspect that draining the bath could cause negative pressure may empty the sink trap so I may need to fit some sort of valve? Another problem is the actual hopper itself. The hopper and waste pipe are mounted on the back wall of the house however there is a conservatory on the back of the house and the hopper is actually below the level of the conservatory roof, hence in the house... sort of. Why it hasn't been moved is a mystery...... Problem is it gets a bit smelly so I'd like to seal it off as the same time as tidying up the pipes. Is there any reason why I cant seal off this pipe? Nothing else uses the pipe or the hopper..