Plenty of water and other drinks to keep you hydrated - that is the best and easiest thing to do. If your BP tablets drain it all out again, then get into the habit of replacing as much and more as you have weed out. When you leave the loo, go to the kitchen tap, pour yourself a glass of water straightaway and drink it. At night, keep a bottle of water by your bed.
You say you eat the right things, so keep that up. Peanut butter spread on wholemeal toast also helps, or anything else with an oily texture.
You could encourage the relevant muscles to be more efficient. The ones in your gut are not very accessible for exercise, but the abdominal ones are. Bending, stretching and twisting all have an effect on the gut contents. When you are enthroned comfortably on the loo, relax, then do some upper body exercises. Bend as far forwards toward the floor as you can, then lean back, then forwards again and back, rhythmically, five, ten or maybe fifteen times. Then bend sideways in one direction and then the other as many times, then twist your upper body so that you face sideways, then to the other side for as many times. This can be surprisingly effective! which is why you do them while in situ (as it were)
I also second the advice to consult your GP.