I'm not entirely sure. I have seen a purple-ish colour in pre-wash water (and/or first Dev) from Velvia, but the water coming out of the drum from Portra was so thick and green I thought the entire emulsion had dissolved!

Going back a stage, I always used to pre-wash E6 reversal films (and Cibachrome papers!) before the first Dev, and it always worked well for me. (It also has the benefit of warming up the reels and film for the first Dev).

I tried the same thing with C41 films and had no problems until I started using Portra. I was quite alarmed by the colour of the wash water, and found that the scans had a fairly strong (but correctable) green cast - presumably owing to the lack of green dye in the emulsion.

What puzzled me was that some rolls of Portra turned the water dark green, but others did not. A further complication was that I had been processing (using a Tetenal kit) at a lower temperature, (30 °C IIRC) which I found easier to control.

I did speak to someone at Kodak Technical Service, who was helpful, but stressed that they had very little experience of manual processing, or processing outside of the normal C41 (at 38 °C) environment. However, he did say that pre-washing was not necessary or recommended, and also said that processing at non-standard temperatures was not recommended, as the activity of the three dyes was only matched at 38 °C.

This didn't really answer my questions, so I took 15 identical photographs on a single 120 roll of Portra 160 NC, and cut the film into four pieces inside the changing bag (whilst keeping my fingers)!

I then pre-washed two of the four pieces of film, and processed one washed and one unwashed piece at both 30 and 38 °C.

The film processed at 38 °C definitely had better colour than the samples processed at 30 °C (both washed and unwashed). However, I could not see any real difference between the washed and unwashed samples, although both were processed together, so there is a chance that dye from the unwashed sample could have made its way onto the washed sample (as the Dev was still noticeably green). Alternatively, maybe the Dev just washed the dye out of the unwashed sample!