Achieving fast oil/water separation in 3D porous aerogel has continued to draw attention due to the ever-increasing concern on environmental issues, but it remains challenging through traditional bottom-up approaches. To address such issue, here a biomass-based strategy is proposed to prepare a tubelike aerogel using bamboo fungus as starting material, a kind of fungi that is characterized by its tubelike stipe with hierarchical porous structure. Through high temperature carbonization followed by physical and chemical surface treatments, the resulting aerogel shows high selectivity toward oils with a rather high absorption capacity of 42 g g−1. Moreover, such aerogel also maintains high oil-absorption capacity even after 10 repeated cycles, demonstrating excellent recyclability and reusability. By virtue of its high porosity and hollow tube that allow for unidirectional liquid transport, a device is then designed to continuously absorb oil from oil/water mixture along with its flow in hollow spite, which is much superior to the traditionally complicated and time-consuming recovery of oil from the absorbents. Given its simplicity and eco-friendliness, such top-down approach has provided an alternative solution to fabricate efficient and robust oil absorbents for fast oil/water separation.