Hi Christopher,
There are many different manufacturers and colours of washes available (have a look at the forum sponsors site
https://www.scalemodelshop.co.uk/).
As requested here is a picture of a wash I use quite often.
Enamels are cleaned up with low odour thinners and you have several hours to go back and work with them, as opposed to acrylics.
Not sure about your Humbrol spray paint, is it enamel based (in which casde the lwo odour thinners you use for the wash woudl attack it)? Typically a clear coat is put down between paint and subsequebt weathering, so if you used an acrylic clear you would then be fine to use the enamels and thinners.
I hope that's all clear, but if not just ask more questions and I or one of the other members will answer.
Cheers,
Bob
Edited to add: When I said you had to be quick with acrylics, what I mean is just work in small areas. For instance, do a single panel line, go back and clean up the excess, then move on to another one. When I started out I was doing an entire panel, by the time I got to the end of the cleanup the wash had dried. That's oen of the reasons I moved to enamels and oils.