Griff, there are anti-diuretic medications that can be used to reduce the volume of urine. Here is a link to a description and a list of brand names:
https://www.drugs.com/drug-class/antidiuretic-h...

Of course, you should check with your father’s doctor before starting any new medication.

I have liner pads I put in at night inside of the pull up. They are unisex and fasten with elastic straps and a button. That catches the most of the urine, and the pull ups get what leaks out. Try restricting liquids in the evenings too.

In the unit we would double up on the adult incontinence products. Sometimes worked. Sometimes didn't for our diabetic residents.