... they hate water (see JB comment), they bleed, some hate sunshine, the ink get's of easy.
I tend too only clean when they are really dirty or smell like a thousand cigarettes.

Pointers: if using water, make it 25° C, not cold and certainly not hotter!!
Dip them in the water with some mild soap, clean shortly, clean of the soap and dry immediately with a paper towel.
Do not rub but dip (ink may come off), just let air dry. If possible the side with the ink upwards.

I have several methods with several types of jetons but most of the times I just leave them in the state they are in.

Hope this helps a bit.

Jo