While you sleep, all the food in your gut is processed and as soon as you wake, you take a huge piss, dumping out any excess water u didnt need, you are completely empty and WAM! You look tight and lean! As the day progresses, you start eating and drinking fluids and WAM, not tight no more. This is only because as soon as you put some water into your body, the body is going to hold onto this water to carry out its daily tasks and keep you functioning thruout the day. The body has no knowledge nor does it care about what you want to "look" like, it only has one task and that is to keep you alive and feeling ok. Then you go to sleep and the cycle repeats itself.
If you want to stay tight and lean, keep carbs to an absolute minimum, and this will prevent u from holding onto too much water