Precoolers for glassbongs screen harmful substances from smoke, thus making it smooth in taste and leading to a reduction of pollution of the lungs. A precooler is usually placed between downtube and adapter chillum. However, if you have a bong with integrated chillum, you can also place it directly between the bong and the glass bowl.
There are not only different forms of precoolers, but they also have different ways of inbuild percolators like diffuser disks or shower head diffusers.

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