The 850 trans has no bottom pan like most cars do. The only cover's in the front and about 1/3 way up from the bottom, no filter, just a valve body.
Although a machine might make the job easier, it can be flushed w/o using an external pump as one uses the trannies own internal pump to pump the old fluid out from a trans cooler line (Bay13 at Volvospeed.com shows this, how it's recommended by Volvo too btw). Nothing remains anywhere in the trans when properly flushed using enough fluid, about 12-16 qts depending on color.