Engine flush

[j90xxx]

Does anyone recommend flushing the engine when changing the oil?
I have changed mine twice (9 - 10k miles each with new filter) in past 12 months, without flushing and oil is black again within days.
Realise the importance of a clean engine (correct oil, turbo problems, dpf, etc) so if a flush is to be done what would the Forum recommend using?
Do Citroen flush when changing oil?
Have read the pdf on servicing, and it is not mentioned. Just importance of oil temperature and drain time.
Opinions, please...

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http://www.stp.eu/uk/products/item/id/52/engine-flush

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And does anyone recommend an OIL ADDITIVE, after changing the oil?