How to Check if a Pipe is a Soil Pipe? Drainage and wastage systems and plumbing help, advice and answers

[Lynky]

I have a small manhole cover in my garden. Inside is a 110mm brown plastic pipe (open). I have poured a couple of buckets of water down it and it has disappeared almost instantly. There is no smell from the pipe but when a toilet is flushed in the house, running water can be heard from this pipe. I am thinking that if this is a soil pipe then I could fit a toilet in my summer house.
Is there a way of ensuring that it is a soil pipe and not just a soakaway/ rain drain?

[jijothomas]

if your soil pipe is blocked you’ll smell an unpleasant odour and notice that your toilet is draining slowly.

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.

[Lynky]

The pipe is not blocked, I just want to know a way of finding if it is connected to the sewage line. I have no more manholes to look at.