Kodak's Z131 document (C-41) explicitly mentions, in bold, not to pre-soak with rotary-tube processing.
I've found out that pre-soak and using stop bath (which is also not a standard C-41 step) helps me with uneven development of large format C-41 film. I feel like there is little point in sticking religiously to the instructions when they clearly don't work (for me)...
Thanks for the Z-131 reference.
When replenishing developer on a small scale.To filter out processing bi products you could pour the used developer through a coffee filter before adding it back into your stock .
I filter my X-Tol working solution from time to time with a re-usable coffee filter.
Not to remove the development biproducts - they are necessary for a properly running replenishment regime - but instead to remove the small amount of sludge that can build up. That sludge is likely to be mostly gelatin.
For clarity: in a properly running replenishment regime, it is necessary that the biproducts be present in a concentration that is stable and consistent. Replenishment is designed to remove any excess of those biproducts, while also replacing any active components as they are used up.