The best drink to flush your system fast is plain water.
Plain water is always the best drink for the body including to flush your system and support your body's natural filtration systems.
Drink normal amounts of water consistently to remain hydrated and keep your system flushed out.
Just avoid chugging extreme amounts of water all at once as overhydration can also dangerously dilute your blood.
Just drink the normal amounts of water through the day to stay hydrated, which will keep your body's system flushed out.
Other good drinks to flush your system other than just water are lemon water or even green tea and even commercial "Detox" drinks.
The over the counter "Detox" drinks cleanses often rely on simple diuretic herbs such as senna or dandelion to make you urinate or pee or use the bathroom frequently, although they can cause dehydration or stomach upset.
Lemon water or green tea also provides your body with mild hydration with added antioxidants, although they don't speed up the natural biological process of flushing your system beyond what regular plain water achieves.
Your body's liver and kidneys work to naturally filter out and cleanse the body.
Your liver, breaks down unwanted compounds, medications and waste products from the blood.
And the kidneys filter the broken down waste and remove it from the body through your urine.
And the water acts as the essential transport medium, which enables the kidneys and the bladder to efficiently push the fluids and waste out.