Exactly. Once you get the fluid back in there and are able to get the pressure up, you will be able to check your connections for the leak. Although you can't find it right now, the fluid had to go somewhere. Just check the hose and your connections with pressure on the brakes. You may be able to put white paper towels or something like that under to try and help with finding where it's comming from. Just make sure you are able to find it's actual leak point as fluid is funny and isn't always obvious.