I mix up my own washes. There are plenty of recipes online, but video related has been the one I’ve used as a foundation for a while.
I somewhat follow the recipe in the description, though for my “nuln” I use 18 drops of black ink, and 8 of burnt umber. For the brown wash I use 16 drops of burnt umber, 6 of sienna, and 5 of black. I think it looks a bit better, but the great part with DIY is how much it can be changed up.
I keep steel mixing balls in the bottles and always give them a vigorous shake when everything is added.
I need to do something similar, I'm probably one of the minority who doesn't have an issue with the new citadel wash formula, but the when washing larger models it gets a bit impractical 😆 I need to bite the bullet and just make a 3l bottle of washes... 😆
I started doing this before the formula change, mainly as a cost cut. I only just recently found out about the formula change AND the bottles are 18ml compared to the old 24ml. I actually had to show somebody my old 24ml label for them to believe me.
It’s quite easy to DIY wash, especially for mimicking nuln. Agrax takes a little experimentation, but I like my personal formula.