Cleaning PVC in Concrete slabs

[Joe B]

I find a lot of green PVC used as Dryer Vents in slab homes and multi story condos where dryer vent is in those floor slabs there as well.
Not debating code issues regarding use.

With my rovac and spinning brushes, I've not had any real problems beside major water removal in some.
I read on several cleaners "service" web sites lately where there is a specific way to do it that is different from other rigid vent.
Anybody have an idea what that might be??

Thanks for any clues.

Joe B