Just read this from 8 Days Nov issue:
"To reduce the amount of carbon emitted during its flights, All Nippon Airways (ANA) launched a month-long trial programme last month passengers on 42 flights to use the washroom before boarding the aircraft. "We are ... making the passengers (a little bit ) lighter," said a spokesperson. According to the airline's estimate, if half the passengers used the toilet boarding, it would cut down carbon dioxide by five tonnes in the trial period. (The Daily Mail also reported that if 150 passengers relieved themselves prior to boarding, this would reduce their weight by 63.7kg.)"
So do the earth a favour. Take a dump before you travel. :)