I have a 1999 Sierra Z71 and theres 2 hoses comming out of the firewall and the plastic connector piece to the right (heater?)hose snapped in two right at the end of the hoseand it almostimmediately drained my coolant. Is this something I can replace myself?

 

yes,those will breakl eventually...you'll have to get 1 from a dealer I imagine...the bitch is getting the old piece off without ruining your heater core....it takes a special little tool....buts cheap...just a plastic lock ring to release tabs.

replace both while your at it