How to highlight panel lines

I would like to know if there's someone out there who could tell me a good tip for highlighting panel lines. I've tried to use acrylic mixed with water and a small drop of washing up liquid and I used the same technique with Chinese ink (on my test model), but I ended up with some ugly stained paint with spots that I cannot wash after it dried. If I wash it when it's still wet no paint will remain on the panel lines. What am I doing wrong ?