Token sinks are useful for countering holding stations; while holding stations can store more tokens than any token sink could absorb, the per-turn transfer limits only slightly favour the holding stations. By passing a stack over a token sink, almost all the excess tokens are absorbed and the otherwise overwhelming effects of a token cascade can be mitigated.
For most practical purposes, tokens absorbed by a token sink are lost for good. Even where some tokens can be retrieved, this usually costs more than the value of the tokens in question.
The Fronsky diagram symbol for a token sink containing retrievable tokens (a cache) is an underlined triangle with vertex pointing downwards. Empty token sinks of varying sizes are implicit to most stations and are not generally marked.