A ladder perc is a long tube in glass bongs that is a type of percolator that moves the water up a stack of bubbler chambers. This helps to cool and filter smoke and vapor, to make the hits much smoother. Due to the design, a ladder perc can collect residue quickly and should be cleaned frequently. The best way to clean a ladder perc is to fill it with a mixture of isopropyl alcohol and salt, shake it up and let it sit for one hour before rinsing it with hot water.