Well, honestly the best way to find out is to just DO IT.
But, for most guys 99% have a major problem eating another mans fluid out of their wife or lover. ESPECIALLY IF THEY HAVE JUST COME THEMSELVES. you get this "post nut clarity" where your mind revolts and tries to throw your ass in reverse faster than the realization you just walked into a southern Baptist prayer meeting.
There is no easy formula to get past that. Unless you have tasted or consumed "the fluid" before. In my case, I admit as a young young I had given head a few times. Hell I even gave a blow job or three in early adulthood. The other thing is there are some funky reactions with a woman's vaginal chemistry post ejectulation. The whole mess smells bad and does not taste like gourmet anything.
You just have to get past it, and keep in mind the idea that pleasing your partner is the MOST IMPORTANT THING.
Now, having said that. There is nothing toxic or harmful in a guys fluid or a woman's. The only risk is Viral or Bacterial. You have to assess that risk BEFORE you ever play.
Bear in mind (and this will piss some people off) Don't stick your tongue up anyone ass. It is a nasty bacteria source worse than a damn rabid cat bite. Yeah your bung hole has lots of nerve endings. But there is a reason they call what comes out, "*******." it will make you sick!
Sorry to be a downer, but contracting Hepatitis or worse just AIN'T WORTH IT.