Simplest and best way to keep water bottles clean and hygienic? Obviously a daily wash with washing up liquid and water is a good start... But with all the use a water bottle gets and the mouthpiece being exposed to the elements whilst cycling through who knows what - are there any other steps you take to ensure your water bottles are clean and hygienic? 

And a bonus question - do you use the same bottle forever, or do you replace them after a certain period?
I wash mine in a dishwasher. Mostly because that requires the least effort.

I've had to replace bottles occasionally, I find that eventually the nozzle on the cap starts to leak.