I share your pain, but I learned to deal with it somewhat. Before you even start on the wash, think about what you are trying to achive. A wash is not a step in finishing that you must get through to get to the next one. For me it is a method to simulate dirt in depressions and make illusions of voids (like tiny spaces between bolt and armor that is really not there in plastic). Apply them only where they serve your purpose.
1. I think first you must find the thinner/solvent that works. TYhe type that will leave minimal tide oily marks. I have not found that perfect one yet, but I have had most luck with cheap hardware store mineral spirit. I went through many types in last two years. The turpentine for me is too oily. I am waiting for an order of Mig's thinning liquid. We'll see how that works.
2. Then try dark brown oil, instead of black. This saved me. Try burned umber. It stayed in solution much better. The bad thing is that it dries matt and much lighter then you would expect, but it works.
3. Finally, I gave up on applying a wash to the whole surface. I use a tiny (5/0) size brush (but about 5mm long to hold some paint) and apply the wash where it needs to be. This was you get a stain with SHARP border - which is not good, but you get no tide marks. I then use a slightly larger brush, damp with clean thinner to blend the sharp edge. This seems like hard work, but it goes fast whenh you get a hang of it. And it does not have to be picture perfect, because it will get covered up with scratches, dust, mud, etc.
4. Also I think to learn, start on a light colored model (not Riussian green or panzer grey). Light yellow tends to be the easiest for me.
Finally, I think the main thing is not patience, but practice...
Here is my balmost finished last model:
And here is the step-by-step of the wetahering:
HTH. I am far from an expert, but I am learning to deal this these issues.