The dirt, feces, dust and bacteria that can attach to your water spout that you will put your mouth is a terrifying thought!
This is a VERY important tip!  Make sure you have a cover for the nozzle of your water hydration system. The trail to Everest is full of animals, trekkers, porters, guides and local people.  The dirt, feces, dust and bacteria that can attach to your water spout that you will put your mouth is a terrifying thought!  Make sure that whenever you set your backpack down on the ground that you have the nozzle of the bladder covered so that you avoid bacteria touching this nozzle.  Also, you can use your hand sanitizer to keep your nozzle clean if it does touch the ground.  Avoid sickness at all cost!