1. Don long-sleeved shirt
2. Lay out tail-washing supplies (towel, dish soap, medium toothbrush)
3. Fill sink with warmish water, put rat in sink
4. Try to prevent, wet, scrambly rat from bolting from sink...just make sure that tail is immersed to soak it for a short bit (minutes if you are lucky
5. Drain water...rat jumps to countertop
6. Put a bit of dish soap between your fingers and starting at the base of the tail, working down to the tip, I rub down and sideways and try to "scrub" in the soap with my fingers. At this point the rat is walking/running around with a hapless human trying to keep up with The Tail...
7. Take your toothbrush, get that tail again and brush in short strokes down the tail, start off very soft and build up pressure if the rat shows no signs of discomfort...think of it as brushing a horse, short strokes...work your way to the tip
8. Take rat in hand, and rinse tail under flowing water...get that soap off
9. Put soaked rat in towel, and dry them off, and return to cage.
10. Clean up area, clean up poops in sink (scrub that sink good!), and nurse scratches...hehehe.
Its not the best method but it really does help a lot.