Regularly give mine a good wipe down/scrub with antibacterial surface wipes, comes up nice and fresh.
Every 4-6 months, or if I spill something on it, I'll stick it in the bath tub with some warm soapy water and kneed it till its clean, rinse off the soapy water and hang to dry.
Had mine for a couple of years now with no issues, still holding together good as new.
Haven't tried it in the washing machine yet, might give it a go next time.