Empty it (obvs) and and flush it through with warm water from the white tip end out the open tap. You can use some gentle hand soap, nothing as harsh as dishwasher liquid. We usually tell people to do that in the shower. Rinse all the soap out. You can use 1:8 vinegar/water to flush out if you think its smelly. Put the cap back on the white tip, leave the end tap open and hang it somewhere to drip dry. Keep it up off the floor.