Flushing cooling system without draining engine block?

So I finally got time to change my coolant. Everything was going good up until the point where I had to unscrew the drain plug on the engine block. I must have tried for an hour to get the thing to turn. I was so happy when the wrench finally started moving until I realized my expensive torx socket was actually bending! So I gave up out of frustration.

After I drained the coolant through the rad (got about 5 liters out) I ran clean water though every hose I could think of. I'm wondering if that was enough to flush all the old coolant out, or do you really have to drain the block to do that?

That is all I did too, just flushed and flushed with water until it ran clear.

yeah just use the flush kit with the garden hose, once it runs clear it flushed 99%