I shoot lots of fake cum scenes with a squirting dildo. I use cetaphil mixed with water about 50/50. So many cum recipes call for an egg white sugar mixture and I personally think that depending where that fake cum is going that a soap mixture is much more hygenic.
I have also used professional makeup slime - Such as found here -
OOZE FX? Stringy Style Slime, Ooze and Goo, Paint and Powder Cosmetics Specialty Products The Paint and Powder Store - this really looks like cum and it doesn't taste like anything, so for cum in the mouth scenes the girls I've worked with really like it. Also very hygenic.