How to seal around soil pipe where it enters the wall

[TriMattRdg]

I have noticed a draft coming through where the downstairs loo is situated.

What would be the most straightforward way I could seal this area around the soil pipe?. Hoping to do it myself.

It's a cavity wall in 1930's house.

Thanks

 

[noseall]

Initially, you want to try and get the foam gun as far into the crevice as possible, but start at the least accessible point, if possible. When set, cut the foam back and fill with mortar.
We tend to re-build around large soil pipe exits, toothing in the brickwork etc. Yours looks like a difficult one though, and a re-build takes skill and time.