I've got some experience with making washes using Pledge, which has inconveniently changed name and appearance in Sweden. Again.
Either way, I've made two bottles of the "magic" washes, in two small medicine bottles I've kept around.
I had two bottles of ink, blue and black, laying around when I tried this, so those are the only colours I've done so far. These are 1 ml Pledge and 4 ml regular tap water with some 10-15 drops of calligraphy ink. Unfortunately, I haven't got any before/after pictures of me using this, but I can tell you that it really sort of crawls into crevices and cracks. It's very low surface tension, so it works wonders as a wash. It's much thinner than Citadel equivalent, so if you're planning on using it to darken metal (like with Nuln Oil) it'll require a LOT of layers, since it hates settling on large, open surfaces.
A useful note is also that they dry slightly shiny. Not the oily-wet shiny of Tamiya Smoke, but not the dull shine of Agrax either.
But I recommend you try it for yourself. The Pledge is dirt cheap and will literally last you a lifetime and you can usually get ink for reasonable prices. In a pinch, you could probably cannibalize a ballpoint pen.