We took a swig from our Sigg the other other morning, and noticed the water didn't taste so fresh. It had been a couple of days since we last washed it. How often do you clean yours?We usually do a quick rinse everyday, then refill it. We only scrub with a bottle brush a couple times a week. We don't want to waste the soap or water, and...maybe we're a little lazy. But then we start to worry about hygiene. How often do you wash yours?