It's really just a rough measurement, I tend to fill my bottle 3/4 of the way with vinegar, then squeeze a bunch of soap in. I'm not scientific about it. Maybe it's closer to a cup(250ml!)... If you do it soap first, it foams like crazy as you pour the vinegar. I doubt the soap matters, I found a recipe online. I get the 4 litre jugs of palmolive from Costco, so that's what I use.
This one says 50/50 with Dawn, but I found more vinegar was better.
https://saraheverafter.com/the-best-...-scum-remover/