I bought two of the Aqua Tainers with the screw on vent at my local WalMart yesterday.  They had 5 of them with the screw on vent.  I may purchase another next week if they still have them.  
As I am planning on putting tap water in them for emergency/camping use should i treat the water with bleach or just put water in them and store them.  I know you should use 10 - 16 drops of bleach per gallon but what is the exact measurement of a drop.  Should i use an old ear dropper to measure it with? Is there a formula so that i can just put in say a tablespoon full in the Aqua Tainers? 
thanks 
Kirby