Two Sewerage reducers in series?

[RecombinantSocks]

We have a Victorian house with a Victorian cess-pit (non-compliant with General Binding Rules - not the subject of this question).
We have found some issues with the sewer pipe leading to the cess-pit and have been working with a specialist drain company to improve the flow to the tank. The system only serves a single 4 bed property.
The original pipe is a 225mm diameter clay pipe and we want to reduce to 110mm to get past some downstream obstructions. At the moment we have done this in stages.
1. a 225 to 160mm reducer.
2. a flexible coupling
3. A length of 160mm PVC sewer pipe
4. A flexible shear-resistant coupler
5. A 160 to 110 level invert, single socket reducer
6. a length of 110mm PVC sewer pipe that discharges into the cess-pit.

Is there any code of practice or guidelines that suggest that the two reducers should be separated by a minimum length of intermediate pipe (160mm in this case)?

 

[Hugh Jaleak]

Is there any code of practice or guidelines that suggest that the two reducers should be separated by a minimum length of intermediate pipe (160mm in this case)?

Nothing I am aware of, simply as it's not a recommended practice in normal circumstances. 9" pipe does seem a bit overkill for one property, just make sure the reducers are easily accessible for rodding, should the line block.

 

[dilalio]

It's non-compliant! Do what you need to do... As long as it works!

 

[RecombinantSocks]

Thanks for the replies. I haven't been able to find any best practice guidance through google but wondered if anyone here knew of anything.
The current setup, as described, is flowing and has been checked with CCTV. The CCTV camera easily traversed through each reducer and into the tank so rodding is OK.