87 yr old male in hospital- thoracentesis was done yesterday only 300 ml was extracted. now they saying they see new fluid build up which looks little complex and may need drainage. is it ok or hospital overdoing?

Newly forming pleural effusions have to be tapped for both diagnostic and therapeutic reasons, specifically if complex appearance, trust the medical team, they are not overdoing it.

Too complex to answer here. Fluid can become loculated into different "rooms" or "bubbles" and may have to be tapped/drained more than once. Finding out the cause would be better way to think of what is going on.