I had installed a Prestone plastic flush tee once. No matter how tight I
screwed the cap on, it leaked. I decided to make a tee from brass. Here was
my method: I located a splicer in the heater hose above the spare tire (most
posts on the subject mention this as a pretty likely choice of locations). At
Lowes in the plumbing section I found the coolest hardware. They sell a
newfangled water line plumbing that is  clear reinforced plastic hose, into
which fit barbed brass fittings plug in and get crimped with a special tool
and metal rings (sort of like our beloved fuel lines). Now you don't need the
crimping tools etc... that was just for the do-it-yourselfers in the
audience. I found a brass tee just the right size which I put in place where
the splicer was, and from the remaining barbed end, I ran a length of heater
hose about a foot long. In the end of this hose clamped a brass plug also
available where the tees are sold. This makes flushing a breeze because the
length of hose is easy to reach. I just unplug the hose, and temporarily
stick my flushing tee into it. (The flushing tee needs to be plugged to make
it into a flushing elbow, or you can also find garden hose ends which work
just as well)