Hi Greeneyesinva,
A persistent cough can certainly be seriously annoying. Other than his catheter somehow irritating a nerve, is your dad possibly taking a blood pressure pill in the ACE-inhibitor class? The generic names of these drugs end in “pril” (captopril, ramipril, etc.). Persistent cough is a very common side effect of ACE-inhibitors, and if he is on one, a switch to another type of BP pill (often an ARB) is definitely worth a try. Sometimes BP drugs in the beta-blocker class can also cause a cough.
In the only article I could find about persistent cough and PD, such a cough is 3x more likely on PD than on HD. Other reasons for a cough could include gastro-esophogeal reflux disease (GERD). The need to sit far forward might suggest this, and so does the food not tasting good. (Stomach acid can burn his throat). Does your dad have any heartburn? Perhaps the presence of the PD fluid is causing reflux of his food, which can lead to a cough. There are a number of treatments for reflux.