You can't totally liquefy it, but you can make it into a usable tea for fertilizing plants. This works with composted cow manure as well.
Take about 2-3 cups of the dry material and put it into a plastic gallon jug with a screw on lid and fill it with water to the halfway point. put the lid on it and shake till the castings are broken up into smaller pieces and the water turns dark. When done, fill the jug to the top and use this for feeding indoor and outdoor plants. This is similar to "compost tea" that many gardeners refer to. They just use compost instead of castings.