Bathroom Puzzle

I'd think if it's got a vent stack then the toilet is (obviously) connected into it under the floor at some point. Dunno about taking the wall down, You'd have to check if it's actually supporting anything above it, or is acting as a brace for another internal wall ??

 

If your loo waste goes straight in to the floor, then it is surely as joinerjohn1 says - it connects into that vent pipe underground, almost certainly as it then bends away to run under your garden or path (any idea what route your soil pipe takes to join the 'main' sewer out on the road?)

So, almost certainly - as far as the plumbing is concerned - you can take down that wall, seal off the hole in the floor where the loo currently flows in to, and connect a new pan sideways into that stack.

Ensure that the waste pipe that joins the new pan to the stack falls downwards at the required slope - consider new floor heights and the height of the pan outlet - fairly standard these days.

And the vent pipe connector will be a swept 'Tee'.

What is the vent pipe made from - plastic or cast iron?

(But don't take down walls until you are certain they are not load-bearing. This one most likely isn't, but it could be )

 

Before doing any thing, I would test your assumptions on the "vent" pipe. I would get up near the stack on the roof and remove the cap from the vent pipe. Get someone to flush the toilet - you should feel the air move in or out of the top pipe with the flow of the toilet. If it is difficult to feel you could try some cling film or similar over the top.

The other thing is to test it, you need to find and lift the man hole cover, then put a little water (coloured squash is good) down the vent pipe and see if it comes out in the man hole.

Never be fooled by the presence of a pipe, several years ago I connected a toilet to a pipe on a new build, only to be called back a week later because the toilet was blocked. It turned out that the pipe I had used was an old one uncovered by excavations and they had accidentally buried the correct one !

 

Never be fooled by the presence of a pipe, several years ago I connected a toilet to a pipe on a new build, only to be called back a week later because the toilet was blocked. It turned out that the pipe I had used was an old one uncovered by excavations and they had accidentally buried the correct one !
Lol! What are the chances!

 

It took us an entire week to find, we rodded from both ends and found an obstruction right on the boundary. Digger came in and dug down 5 meters and then realised that they had lowered the road 20 years previously and had to redirect the pipework ! but to where. We then had to track down a previous owner who told us where we were looking in the wrong man hole ! He told us where the correct man hole was and then sent a jetting tool down the pipe - it was like striking oil, a huge plume of mud and water came out of a spoil heap.