External waste pipes angle problem

[bobasd]

The AAV is incidental to your drainage problem.
The 150mm is a precaution in case the fixture gets flooded to its "flood rim" - which is one problem you dont have.
However, its as above noted, too low and needs say a 1500mm min stub of soil pipe above the Tee.

 

[bobasd]

In the new pics the render is left stopped above the lower exposed brickwork leaving a water trap ledge that could lead to interior damp.
You definitely need a Bell Cast there.
BTW, all Bell casts and beads such as Angle beads should be in non-rusting plastic for external work.

There's no Access Fitting at the base of the soil pipe - they should be installed for using if rodding or jetting is needed. But leave alone until needed.
Its possible that the gulley trap is discharging into the soil pipe.

 

[denso13]

AAV's should be fitted a min say of 150mm above the flood rim of the highest fixture

Not if it is a type A1, if so it is fine where it is.

 

[bobasd]

Agreed. I was wrong. I got over my toes.

 

[cdbe]

It's blocked, probably with tile adhesive or plaster if you've had "builders" in or a giant hair ball, not helped by the dip in the middle but it would still flow if clear (it flows round a u-bend a bit further back under your bath) obviously with a higher than normal risk of future blockages. Unfortunately it's solvent weld but you could try one of those mechanical unblockers, like a steel coil. You may be able to get it in from the top of the stack if you remove the AAV or even drill out the boss on the other side to gain straight access (you can blank it later).
My big drain rod set has a half moon attachment for scraping the bottom of pipes, I don't know whether you can get similar for smaller pipes?

 

[bobasd]

There's a sag in the pipe centred on the outlet/clip - the waste comes out falling and after the outlet/clip it rises slightly to the boss - the pipe should be replaced.