HotSpring pressure tests and water tests each spa. They use heated, chlorinated water which is filtered and kept clean. They have to - workers' health and the ability to see all jets working require clean clear water.
Once the test is done, they recycle the water by drawing it out of the spa through filters and returning it to some tanks.
Then the spa is dried out as completely as possible, including blowing out certain systems and applying suction to others. They even use good old-fashioned towels and such. BUT - there will still be some areas of the plumbing which will hold water.
We (talking about my stores) follow the factory recommentation to do a chlorine shock as soon as we fill the new spa in it's new home. Takes care of the whole thing quickly and easily. And the customer will not be getting in for a min of four hours anyway - longer for a spa running on 110 volts
.