I prefer the bladders from boxed wine. They are very durable, and come in 5 and 9 liter sizes. When empty they roll into a package about 2x4 inches weighing only 2.5 oz for the large size and a little less for the 5 liter. So they are easy to pack out. And they are free.

I cash them away from the trail and out of sight, and camouflage them with pine needles or other leaves. Since they lie flat, they are easy to hide. In the desert, I cover them with piece of khaki or chocolate chip camo cloth.