I refueled the Pa28 I was going to take on a 2 hour round trip including 10 minutes over water and didn't wait the requisite rest period before rechecking the fuel drains. All the moisture that had condensed overnight on the insides of the (nearly empty) tanks took about 30 minutes to reach the carburetor by which time we were cruising at 4500 feet.
One precautionary landing later followed by a careful run up and test circuit at the airfield I had diverted to we returned home to tell the tale.
The lesson: if you can top up the tanks the day before you leave, then do so. Otherwise, wait at least 30 minutes after filling them in the morning before you test the fuel drains, especially if the previous night was a cool one and the aircraft lives outside.