I think your father is having pleural fluid in the chest cavity and not adcitic fluid. In my opinion it must be due to spread of lung tumour in pleura. Better to go for pleural fluid examination for malignant cells. And if this is positive go for Intercostal Chest tube Drainage (ICD). Drain all fluid and than get done pleurodesis by talc. Talc pleurosis is the procedure performed by pulmonologist and this is indicated in recurrent pleural effusion like malignancy, recurrent pneumothorax etc. In this we arteficially creat inflammation between pleural layers by injecting talc powder through ICD tube. So both pleura adhere to eachother and no space left for fluid accumulation. This is just an option on which you can think. So consult pulmonologist.