ummmmm... Are you a fencer? That's kinda a gross question. What the hell made you ask that? ewww. You should really polish up that sentaence so it has a little more tact. yuck!!!
Crude question but the answer is yes you should. It won't really make you lighter but is will make you more comfortable if you don't have to suddenly go during the middle of you DE bout....
If you give a man a fire, he is warm for the night.
If you set a man on fire, he is warm for the rest of his life.
The answer to your question is "go if you have to go whether it's before, during, or after the tournament". If you are really interested in being lighter for a tournament, then begin a weight loss program with a healthy balanced diet and exercise. You can only lose some much weight from defecation.
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Lumberg.
"...ahhh, we have sort of a problem here... yeah, you apparently didn't put one of the new cover sheets on your TPS report"
Are you getting your 25 grams of fiber a day???