Smell problem from toilet

[SteveLydon1]

Hi I'm looking for some advice on a problem I've got - my toilet is directly above a utility room. If you are in the utility and someone flushes the toilet there is a smell of sewage in the utility. The smell only happens when the toilet is flushed and then goes away. Both rooms are next to an exterior wall and the waste pipe from the toilet run down the outside of this wall and goes underground right next to the utility room.
I'm not sure what could be causing this or where to get advice or help to solve this as its quite unpleasant as you can imagine.
Any help would be much appreciated - thanks
Steve (Notts UK)

 

[Hugh Jaleak]

Is there a sink or washing machine in the utility room? Any waste pipes connecting to the stack from those?

 

[SteveLydon1]

Is there a sink or washing machine in the utility room? Any waste pipes connecting to the stack from those?

Hi Hugh, yes there is a washing machine in the utility. This drains through a different wall into a grate on the back of the house ( stack is on side of house)

 

[Hugh Jaleak]

Hmmm, not so sure then. Nothing else in there obvious that could give rise to the problem. Have you lifted any manhole covers in the vicinity? Smells are sometimes first warning of a problem underground. BTW how old is the property?

 

[SteveLydon1]

Its a 1930s semi. Am I right in thinking the waste from the toilet is a separate pipe from the others in an older property? The waste stack is on the outside by the way.
There are two manhole covers on my property but I think these are for the drainage for the kitchen/bath etc