Our effluent waste and stench pipe is located insisde our house. We live in a heavily attended tourist area with a sewerage works catering for a low local winter population that rises from 2000 in the winter, to 19000 in the summer and at peak times of the day - 8.30 am amd 7.30pm some terrible odour emanate from our internally located sewerage outflow srench pipe. I assume this is some sort of backflow of odours from the mains at peak times but the smell is overpowering, the pipe is in our kitchen and I don't know what to do. The pipe was obviously there before the extension was built round it at some later period and it has got to be unhygenic.
Any suggestions on the legality of internal stench pipes and possible explanations of what is going on - is it repairable would be very gratefully received.
Thank you :)

That stench pipe is aptly named a sewer vent stack and should continue up through the roof and then terminate.