You say you had 2 operations so far and are looking at having a third to correct asymmetrical descent of one AND get smaller (than 425cc) implants either by removing saline from your present implants or putting in new ones.
A few comments -
1. ALL breast implants droop. The heavier the implants, the weaker the breast tissue support, the faster the droop.
2. All breast implant shells ripple. Saline implants ripple MORE than gel implants. UNDER filled saline breast implants ripple the most and leak / rupture the most.
From your description, to restore symmetry and have implants sit at the same level, the shelves of breast tissue on which the implants sit must be level. This means the sagging implant needs to be removed, the support shelf repaired at the higher level to hold it and the implant / another implant placed back.
Yes - saline CAN be taken out of both implants. BUT - this potentially could worsen the ripples of the shell (= hasten the date of deflation) and potentially introduce infection to the implant.
In other words, it MAY work but more likely, it just pushes the decision of replacing the implants down the road when they either deflate or, potentially, become infected (a MUCH worse complication).
I hope this was helpful.