[header] How to clean hydraulic fluid from asphalt [title] Cover the area with cat box litter. [step] Cat litter is made to be ultra-absorbent, and it can soak up a lot of the hydraulic fluid, drawing it out of the asphalt. This works best on a fresh spill, but it can be an effective first step at treating hydraulic fluid which has soaked in, as well. 
[substeps] If you prefer, you can use another absorbent material, like sawdust or granulated clay. [title] Use a push broom to spread the litter over the stain.