Hi, a sceptic tank has been installed in the estate up the road. We keep getting very very bad sewer smell at certain times of the day. It has been confirmed that this is when the tank is being emptied. My house is old and previous owner in their wisdom ran one of the 3" cast iron rain water down pipes directly into the sewer without a trap. We suspect this where the smell is coming from. I have thought about installing a rat trap (flap) valve where clay pipe comes out under inspection cover-but end of pipe is complex shape so could only fit inside and have not been able to find one. No possibility of fitting conventional trap or drain because bottom of vertical cast iron pipe is embedded in stone arch. So looking for a device that can be fitted into vertical cast iron pipe possibly or any bright ideas? Willing to make or adapt something if anyone has any experience. Help would be much appreciated. It is a very bad smell!