How do you put that bladder onto that little hole on my fp7125-04 tank?

http://www.depcopump.com/datasheets/flotec/FP7100,FP7100H,FP7110,FP7110T,FP7100TH,FP7120,FP71 25,FP7130,FP7135_manual.pdf

Check this out. It looks like there is a port on the bottom that comes off. Worst case scenario... call this number: 1-800-365-6832

Follow the directions on the instruction sheet that jlisenbe shows in his post. Remove the bottom piece, insert the bladder and inflate. Good luck, tom