i drank 500ml as it said on the form cause they didnt tell me how much when i rang. about 1/4 the way through the scan i had to go let out 10sec worth but i coudlnt stop it so it was like 15sec lol. then towards the end they coudlnt get certain shots so told me to go let it all out and they sid it was perfect and next time not to drink anythign just wat i normally would in the day