You can't. It takes time and effort to lose weight.
Think about it really hard and look at your question again. It is 3 days in case you did not get it.
Yes, you could lose 7 lbs after a bathroom break if you excrete enough water and waste. Burning 1 lb of FAT in a day? Virtually impossible.
0.08272222 Earth days equal one day in Ceres, if I'm not mistaken (Witch I usually am)