hoover proheat plus steam cleaner leaking water everywhere?

I bought a used proheat steamer and downloaded the manual before I did anything. I rinsed out the water container and cleaned the little red filter area out. I then filled the bladder and put it in the machine and put the handle in the locked position . Well, water started to pour out of the bottom of the machine until I removed the tank. I again emptied it and started again. Same thing happened. What am I doing wrong? Thanks ahead of time for your response.