vinegar .. and water but if its too dilute they will throw it out .. best thing to do is buy "strip" from local head shop sure its like 40 dollars but i have used it on several occasions when i was looking for a job passed every time and i used it at least 7 times positive results and not positive for marijuana lol they have 300% guarantee they will double your money back and send you free product if it fails undetectable as far as i seen ..