AR ONE leak behind toilet question

So I put on my cheaters to try to get a better look, it's such a tight space to see behind, and realized that the leak was at the connection where the plastic pipe screws onto the back of the toilet. I unscrewed it and inspected the gasket. The gasket seemed fine so I screwed it back on tight and so far I haven't had any more dripping. I don't understand why water would be in the line all the way up to the toilet since my tanks are empty? I even tried to cycle the toilet flusher to release this water. Does this line have a one way valve or something similar that prevents the water from flowing backwards into the holding tank or is it the design of the water pump to hold the water after its pumped through it? As far as posting pictures goes I tried reading the how to section but it's all foreign to me. I'm using my cell phone to post here but can't figure out the deal with the public website thing or the copy and paste thing. I don't see any icon that would indicate posting a picture. Thank you all for your replies.