IDK about the BX. On my MX I nearly had mine changed with only about a cup of lost fluid, then I fumble fingered the filter and ended up losing about a quart.
It's been a minute (5 years or so) since I changed the hydraulic oil and filter, and cleaned the hydraulic oil screen on the BX25 that I had. I don't recall losing much if any oil so that jives with what @whitetiger stated above. The screen should be cleaned and inspected.