3 liter bladder, so it carries plenty of water. Outside stash pocket is the perfect size for a rain jacket. Its big enough that I can get a change of clothes (sans shoes, I leave an extra pair at the office) when I commute back and forth to work on my bike. Loop on the back holds a flashing LED real easily, great for being seen at night. Never had any leaks from the bladder.
The main compartment can get a little tight. The bladder's opening screws down fairly easily, but is killer hard to open... never had it leak though.
I have an old style Mule about 7 years old so it's a little different. 100oz water capacity is great for the long hot rides or fill with less water if just doing shuttles.
The screw on cap is brutal to unscrew as mentioned earlier but does not leak. It will leak if not tightened properly.
To fill bladder just lift it up enough to expose the cap and pour water from your Brita in.
When the straps turn pure white from sweat just toss it in the washing machine. This is when I usually clean the bladder with Efferdent tablets they work great!!
After over 7 years the velcro closer for the bladder storage wore out :0