It may well be promoted as a ‘self cleaning’ medium, but this is likely a market ploy.
The hydrostatic capsule is filled with what is commonly known as ‘ectoplasm’ that, it can be said, replicates the effects of amniotic fluid while also providing a medium for a kind of suspended animation. Here is an excellent layman’s video on amniotic fluid to give you a tiny insight into the potential nature of ‘pod goo’.
https://www.youtube.com/watch?v=zjD9Ky4zFME
Scientifically, any liquid medium cannot simply ‘clean’ itself in anyway from solid or liquid contamination, and the human body even in low activity continues to shed skin tissue by the cell-full. It also requires the evacuation of waste products such as urea/urine and faeces when solid food is consumed, as well as residual oils, waxes, mucus and other secretions that are constantly pumped out by glands around the body. The vast majority of these occur even in a state of unconsciousness, such as in a coma or in hibernating animals, even if at a reduced rate. What is required is physical filtration, or a medium with the capacity to effectively dissolve all of these waste products (to a finite saturation amount) which would still require periodic replacement.
Solids can be made ‘self cleaning’ by being hydrophobic and repelling a lot of water based dirt issues. Liquids, by their scientific nature, cannot.