I hope it doesn't come out too harsh, it certainly isn't meant this way... but this trick to make washes has been known and afaik widely used for quite a few years now

. And as has already been mentioned, there are more effective ways to achieve the same effect.
That said, this trick gives you washes, not inks. Inks (I use Daler-Rowney FW) don't feel like they're just diluted paint with soap/flow-aid. They don't look like it either. Seems to me that inks really are differently formulated/pigmented and that you'll need more than a nifty trick to make some
