Similar to the tell-tale signs of a leaking soil pipe, if your soil pipe is blocked you’ll smell an unpleasant odour and notice that your toilet is draining slowly.
If you’d rather not complete this messy job yourself, contact your local plumbing engineer for help.
If however you’d like to attempt to remove the blockage, ensure you wear protective clothing and a facemask.
If your soil pipe is made of cast iron, it’s likely that it will be cleared via the vent above the roof and it’s unlikely that you’ll be able to gain access without the advice of a professional plumbing engineer.
If your soil pipe is modern and made of plastic, there should be a large hinged cleaning eye, or other access plugs, wherever the branch pipes join the stack.
Unscrew the cleaning eye and insert a drain auger. Also known as a “plumber's snake”, "toilet jack" or "electric eel", a drain auger is used to remove any plumbing blockages that cannot be dislodged with a plunger.
Pass the drain auger through the pipe until you find the obstruction. Then simply crank the handle to release the coiled metal wire inside the auger. Push and pull the auger until you manage to successfully remove the blockage, clearing any trapped water.
To clean up you’ll need to hose the stack and disinfect the surrounding area.