i just have a simple question about PEG tubes... it bothers me a lot cause im confused about a J/G tube... PEG tube... whats the difference?

i ask because im browsing the threads for someone maybe having a tube like mine. it has 3 ports. GASTRIC, JEJUNAL AND BAL.

the radialogist who changed my peg ( just 4 days ago ) told me to use the Jejunal port for food intake and dont mess with the other two. im new using this tube, coz the last one i got only has 1 port. all goes into there. now i got 3... and on the gastric port i can see that there is a yellowish fluid inside the tube. (the tube is clear by the way) i dont know if i can flush it water coz it bothers me. and that being said, what is the purpose of that gastric port anyway?
im havng some stomachache lately... its feels like air is in my stomach... im thinking maybe open the gastric port and hoping my stomach pain would go away =(