I think you’re refering to the final clean out after you are fairly confident the drum is cut. Ive personally cut approx 80 – 100 drums and found the best practice for a final cut would be to move up slowly from the very bottom. Look for 3 things 1) if possible maintain visual contact with the chute and look for clear water. Any sign of black means you have more coke….clean this out and start over at the bottom. 2) Listen for the water hitting the wall. 3) pay close attention to your drum temps…a rapid conciderable temp drop is a good indication of that section of the drum is clean. REMEMBER: none of this as an exact science. Experience is your best protection against leaving coke in a drum.