How much water does the bag hold?

The bag holds 2 quartz of water.

How do you hook the bag to the back of toilet or sink it came with no instructions

Thanks for reaching out! You can find instructions here: https://cdn.shopify.com/s/files/1/0240/6504/8681/files/P708_Inst.pdf

In terms of hooking the bag, it does have two holes at the top. You can use nails to hook it to the wall if needed. Or use a suction cup with a hook and attach it to the back of the toilet.

Hope this helps!