In article , Robert
Borucki wrote:

I flew a Cherokee Six PA32-300 and finished up the flight and topped off all
four tanks. Then noticed, an hour later that there was fuel streaming from
the overflow port under the left main tank. The left outboard tank was 3/4
drained, and all other tanks were full. The fuel selector was on the right
main at the time. Any ideas what the problem is? I thought all tanks were
separate, but it appears that the left outboard may have drained into the
left main and overflowed......

Was it outside?
Was the sun shining?
Did you open the cap to vent the tank?
Tell the fueler not to fill it all the way to the top if the aircraft
is going to be parked outside in the sun after fueling.