The pressure in the system holds the car up, the rear end will drop down when you remove the hydraulic lines, and even it if was up on ramps, it makes me nervous to have the car move around while I'm under it. Much safer to have the car suspended with the wheels free. It drops down pretty far with no hydraulic pressure.
Doesn't matter which line you remove first, all the pressure blows out that one. The other reason to have the rear wheels hanging, far less pressure in there.
The filter is in the fluid reservior up front, or in the pump, I didn't change mine.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!