The procedure Derek Ashby showed me was to pump out as much as possible and the last bit you vac out angling the hose end so you maintain a high input of air.
Got my biggest job to date on Monday only wish I had more heat, pressure, suction and less fannying about.
Worked out Ashby's mods to my ninja to TM it come in at over £2k so I will be pumping and sucking for some time, and then I've still got to empty the solution tank.