Too much salt in the diet can affect water retention *to a degree* especially with kidney function impairment, which is common in diabetics. You might want to ask if there are any specific dietary changes needed.
Ask your doctor about compression stockings to keep the fluid out. When you don't have to stand, sit with your feet up, and whenever you can, put your feet above the level of your heart to help drain the fluid. Check with your doctor, but I'm pretty sure you should be following a low sodium diet to help. Definitely check this first with your doctor, but they may want you on a fluid restricted diet, in which case drinking extra fluids would be harmful. DO NOT change up what you've been doing without consulting someone who actually has a degree. It's just something to ask them about.
Make sure you are actually taking the water retention pills correctly--go back and reread the patient info, or go ask the pharmacist to describe it in detail to make sure you aren't missing anything. What pill are you on?