[Marco B]

I have been in between sort of a change from flowing water to standing water (as I have sometimes problems with water quality).

During that, I have monitored washing quality using HT-2 and to my very big surprise, there's no stain in the (sheet) film after only one or two water changes (15 liters per change).

Film probably just needs far less washing than fibre based paper. Remember that your sheet film is made of pretty water impermeable polyester, versus the water soaked and contaminated paper base of a fibre based print. That probably makes a huge difference..., as the gelatin layer on the film base is just a tiny layer.