Some people use apple juice to dissolve the Epsom Salts in, rather than water or grapefruit juice. If you are asking about mixing the olive oil with grapefruit juice, you can use lemon juice instead of grapefruit juice. Most people drink the oil and lemon juice separately. I mix them together just like the grapefruit juice and it works great. I also sometimes use the juice of one lemon and grapefruit juice with the olive oil, all mixed together and that works very well and the lemon juice seems to be the predominant flavor. The purpose of the citrus juice with the olive oil is two fold. 1) It helps emulsify the oil so it isn't icky oily when you drink it. 2) The sour flavor somehow stimulates the bile flow.

Orange Juice and any number of different oils

I have done many successful flushes using apple juice. The first flush I ever did was recommended by my doctor and it used apple juice. If the juice is real sweet I do add the juice of one lemon, that seems to help.

The real advantage of grapefruit is that it mixes so well with the oil. Apple juice separates quickly, so you have to chug the drink pretty fast; although a chaser of more apple juice or even a swallow of real Coke helps cut the oily feel in your throat.