is there a trick to clean a hat?

what kind of hat? for a normal cotton baseball cap, sink of cool water with a bit of mild detergent, soft toothbrush on the sweatband (that's where the grime is), rinse, then dry it over a bowl or a rolled towel so it keeps its shape. never the dryer. older caps sometimes have a cardboard brim, so don't soak those, just spot clean. wool or felt hats are a different job, no water, use a hat brush.