I replaced the fill valve in my toilet a week ago. Now I can flush the toilet and the tank fills... all is good, but when I go back an hour later the tank is empty. All the water is gone. I've tried adjusting the syphon tube but that doesn't help. I can't figure out were the water is going. Please help?

Sounds like you're digging through the flapper. Replace the flapper and see if that doesn't help. Let me know how you make out. Good luck, Tom

I agree with Tom your flapper needs to be replace open the link and watch Youtube, good luck.

John

How to Fix a Toilet - Flapper Valve Replacement - YouTube (http://www.youtube.com/watch?annotation_id=annotation_613568&feature=iv&src_vid=Suno4wxDNk0&v=3W3u2O1dZws)