Can I lose weight using laxatives and diuretics?
The short answer is yes you can. And a number of people with eating disorders have done just that.
It works by moving food through the gut faster, leading to malabsorption. Thus the body absorbs fewer calories. However, it also means the other nutrients that the body needs are not absorbs either.
Overall, I would not recommend this method, though. For one, your body will lack vital nutrients as it expelling them. And two, long term use of laxatives can harm the digestive tract, leading to incontinence and a lazy bowel.
Diuretics are a short term solution. It causes the body to expel water via the kidneys. Some of this is subcutaneous water that makes us look fluffy. But none of the weight lost via this method is fat. Diuretic use is also banned it a number of sports, as it can be a masking agent for a number of PEDs.