I went to change my coolant on my 1998 Subaru Legacy GT because it was low and my radiator draincock, or petcock was snapped in half. I went to get a new one at the auto parts store and got home and it doesn't fit. It looks about the same size but the new one is slightly longer. It starts to thread and then pops out. I tried other auto parts stores and had no luck. Any ideas?

Find a bolt with the correct threads and plug the petcock hole, you don't need it. To drain, remove lower rad hose at thermostat housing, Messy but fast. To refill connect lower hose & remove upper hose from radiator.  Pour antifreeze directly into upper hose until antifreeze is at upper hose (your block is now full) connect upper hose to rad, then fill radiator.