Can cabin pressure be lower than outside pressure? In order to allow adaption to changed pressure, the pressure change in an aircraft cabin is stretched out over time. My observation is that the cabin pressure drops even before the plane takes off, and has not yet reached ground level at the time the aircraft lands. This would make sense, allowing for longer adaption times, but needs better sealing which is able to work both ways.

My question to the systems specialists: Can an aircraft cabin have a lower pressure than outside, and is the technique of stretching out the pressure change as explained above actually used?
Besides the sealing the aircraft would also need a vacuum pump that is able to pull air out of the cabin which means extra weight.

The way aircraft maintain cabin pressure is through a air cycle machine that pushes air into the aircraft and outflow valves. There is no facility to pull air out of the craft. 

Any pressure drop you may experience on the ground is probably because the pilot increases air pressure on the ground slightly to test the seals and then releases it before takeoff.