It all depends on what your clear coat is. If it is an acrylic, use and enamel wash, or vice versa. Or if you have access to them, try promodeler washes. That stuff is great on the few I have used.
I use the “soapy” acrylic paint wash. It was in one of the FSM articles a few months back. The soap allows for easy clean up after the paint wash has dried. The panel lines really pop. If you mess up or don’t like it you can clean it easy and start over. I have been using craft paint I picked up from Wally World for .98 a bottle. I have a burnt umber, raw seana, midnight black, a neutral gray, and white.
I mix the different colors for the effect I am looking for, (ie more of a gray/black for modern Navy A/C.) with some dawn dish soap and water. I then apply it to a “practice” wing I have for consistancy. It works for me.
I tried a few things but what worked best for me was a mixture of soapy water and technical pen ink. It fills in the panel lines well and is easy to clean off the surfaces I don’t want it on.
Rather than soap, you might want to try rubbing alcohol for a “wetting agent”… Be sure to test it first though. Some acrylics don’t like it (Like Vallejo, but Tamiya and Model Master seem to love it)… Alcohol evaporates faster than soap…
On the subject of soap it does more in the wash than act as a wetting agent, it also weakens the paints bond allowing for easier clean-up as you are already finding.
I believe we established that you are using a non-acrylic clear coat, so DO NOT use this information if this is true, but if you use an acrylic clear coat, such as future floor polish, let me say this. I use trupenoid, a derivative of turpentine. I fill a bottle cap with it and swish a drop or two of artist oil burnt umber. This, spread on with a thick brush, is really self-working, the flat areas require little to no cleanup. But remember, this is only for acrylic clear coats. One other thing, if you aren’t using them, I would consider using an acrylic clear coat because acrylic washes have a nasty habit of looking nice and wonderful when wet, and almost disappearing when fully dried. Oil washesare the opposite, they look better AFTER they dry. So, that’s my two cents on this subject! Happy Modeling!