think some use talc, i have seen some inserts you can use to help soak up the sweat or it has been suggested that you stick a panty liner in the front of the hat !!!
Just fill a bowl with hot water and laundry liquid, give it a few good scrubs with a brush, rinse it out well and hang it in the airing cupboard to dry. Worked a treat with mine, although the smelly grey water after I'd finished was quite disgusting to say the least!
I think both Charles Owen products work a treat - I use the cleaner and the deodoriser from time to time and they bring it up good as new! And the cans last forever.
My champion one I take out the padding bits and wash it in warm water and soap and give the padding bits a good wash too then leave to dry. My Harry Hall one doesn't come apart so I just wipe the inside down every other time and leave to dry - sometimes I rub a little bit of fabric conditioner inside to keep it fresh.