Always be very careful when working with hot water. Sharp scissors have to be used to cut the bottles, if you have a ragged cut edge on the bottle it may scratch fingers and hands. Care should be taken at all times. Punch or drill air holes in the lid. Cut around bottle 2 as shown.
Air vents help to encourage aerobic decay in organisms.
Stick the tape over the hole in the bottle. Cut around bottle 3 at the widest point. Make 3 vents as shown in step 3. Punch or dirll holes in the lid of bottle 3 and use a piece of old tights as a filter. Cut bottle 4 as shown.