I did a saltwater flush yesterday afternoon, which is basically a laxative drink.
All you need to do is mix 2 teaspoons of sea salt (probably available in supermarkets, I bought a pack at a health food store) in a litre of warm water and drink.
Taste: Well, it's not great. After all, you are drinking warm salt water. But it's unpleasant rather than horrible. The salty taste does linger in your mouth for a while afterwards.
Quantity: I only managed to get through about 800mls. You do start to feel quite bloated. Will have to drink the whole litre next time.
Effects: Took a bit longer than I thought to work, probably took me about 30 minutes to drink the 800 mls, then about an hour before I started feeling any effects. Keep this in mind if you are doing it in the morning and have to go out! Then it was one trip to the bathroom, and after about another 10 minutes, a second trip. That was it for me.
Overall, not a bad experience and I will do it again.