This version of the passive voice is perhaps the hardest.

The Past Perfect Continuous Tense

had been (doing something) + (time)

– examples

(By the end of last year, the company had been selling books for 10 years)

The Passive Voice

To make the passive voice:
be (in correct tense) + p.p.

So, for the past perfect continuous tense:

had been being + p.p. (+ (time))

– example

By the end of last year, books had been being sold by the company for 10 years.

Examples of the Past Perfect Continuous Tense in the Passive Voice

(active) The bank had been losing a lot of money before the new manager arrived
(passive) A lot of money had been being lost by the bank before the new manager arrived

(active) She had just been walking the dog when I first saw it
(passive) The dog had just been being walked when I first saw it

Exercises

1. Change these sentences into the passive voice:
(i) He had been building the website for 3 years before he got any funding.
(ii) United had been beating City for years before the power changed.
(iii) The boss had been interviewing candidates all day before, finally, a good candidate arrived.

2. Change these sentences out of the passive voice:
(i) The dog had been being walked for an hour when, suddenly, it ran away.
(ii) The company’s money had been being stolen by the boss for two years before anyone noticed.
(iii) The law made it legal to wire-tap; however, the people in the city had been being spied on by their government for years before that.