Alcohol, smoking, caffeine, junk food and dairy are all the worst culprits for funking up your downstairs flavour.
After that, garlic, asparagus and broccoli are known for making ejaculate taste stronger/more intense.
Before drinking gallons of pineapple juice (which only really masks bad taste) the best thing to do is cut out all of the above first. That should sweeten the taste anyway as cum is naturally sweet.
If you still fancy a little extra customisation after that, THEN you can start playing around with fruit juices and smoothies to tailor your taste.
Best foods to lighten the taste after you've removed the toxins from your diet are pineapple, kiwi, watermelon, parsley and cinnamon.
Drinking more water will increase the quantity, but make it less thick. Also, how freuqently he's ejaculated will make a difference. If he hasn't cum in three days, his cum will be stronger, thicker and there will be more of it. If he came yesterday/earlier that day, it will be "fresher", less viscous and there should be less of a mouthful.