Hi Chris,
I generally wash with artist's oils thinned with Humbrol brand enamel thinner, I find it just work better for me that way. I have used acrylics to good effect, but artist's tube acrylics, not hobby paint.
The problem you're getting is from using water as a medium. Used straight it has too much surface tension to flow properly. In theory the detergent should fix that, but it doesn't work for me either! I use 'Rubbing Alchohol' from the chemist (drugstore I guess
) as a medium for acrylic washes. Rubbing alchohol is 70% Isopropyl and gives the acrylic wash the same 'feel' as the oil washes I generally use.
Hang in there, you'll get it!