why is my truck leaking coolant/anti-freeze?

What is your question?

my 2004 chevy trailblazer was leaking coolant so I figured since I had a big hole in the top of my resivoir that it needed to be changed so I bought a new one and got it put in but its still leaking from the same spot(the back, there is a hose in the back of the resivoir) I don't know what IS causing it. the old one was not hooked to anything so I didn't hook this one up to anything. any suggestions????? it happens all the time, it don't matter if the truck is running or not it still drips out.