Right - of course. But it doesn't have to be done it that way. It is simple enough to just not put fluid into the canister of the power bleeder, but rather top off the MC, pressurize, and bleed a wheel or two until the fluid level in the MC starts to get low (just as would be done with the second person method). Then de-pressurize, top off MC, re-pressurize, and continue. This method of using a power bleeder uses no more fluid than the two-person manual-pump method, and the power bleeder remains clean, as the fluid never comes into contact with any part of it, other than maybe the inside of the reservoir pressure cap.