i have a 1992 2500 with a 6.5l td(first diesel ever owned , learning project )

my question is , what does the T valve do and how does it help me bleed the system? also should it be in the closed position or the open when running ?

i tried to bleed my fuel filter and nothing but air came out the whole time maybe a little fuel but nothing like it was at the T is this normal ?


thank all of you for making this a great place to trouble shoot and learn!!!!