depending on the type of look you're going for you can make several different types of washes (inks, glazes, dips, etc etc).
I personally make most of my own because I can get the color I want and I can make a large enough batch to do an army or several armies.
Inks can be made from things like acrylic artist's ink and such. When I mix it up, I will generally add a drop of Color Float per ounce of fluid as this breaks up the surface tension of the water. I get it to the strength I need it by mixing more or less water in it. Usually the ink by itself is way too strong.
There are a couple different ways you can make a glaze. First, the traditional glaze which I've used a LOT is generally either a watered down paint (usually I thin it slightly with Future Floor Finish or Vallejo Glaze Medium) with some Color Float. Some people will also add some ink to it (GW, P3, Vallejo) to get the color they're after. It's great for flesh washes. It gives a nice effect without being too strong.
Another way to make a glaze is to use something a bit thicker than Futur Floor Finish or Vallejo Glaze Medium. I've found this stuff by Delta Ceramcoat called All Purpose Sealer. It has a good consisitancy and takes either paint or ink well. You can also get seomthing called Artists' Acrylic Medium at most of your Hobby Stores (Hobby Lobby, Robert's, Michaels, etc etc). Depending on how strong/dark you want it will vary the amount of paint/ink you add to it. For another way to do the flesh wash add about 12mL of ink or paint to a 8oz bottle. Add a drop of Color Float per ounce of liquid. Shake well and enjoy!
Now for dips! This is something most people either love or hate. It can be made by mixing Future Floor Finish with a color of paint. Most of the time, I've seen it in black as it's usually the last step done to finish a model. To make it, you'll take a bottle of Future Floor Finish and empty it into the container you'll use for your dip. After that, you'll take a well pigmented paint. I have seen things as far as Craft Paint, GW, Vallejo and even tempera paint used for this. After it's mixed, add your Color Float (1 drop per ounce, but it's not crucial to get it measured EXACTLY). Once everything is together, make sure it's mixed well. Afterwards, you have a decent quantity of dip. If you're wondering why it's called dip, it's because you dip your models in the liquid instead of painting it on. Future Floor Finish will dry to a glossy color so be sure to matte coat it once finished.
I hope this helps!
Thomas