If you want to despawn your pet by sending it at blackfuse until it ranges you, you have to make sure you are close enough to Blackfuse when you tell it to attack. I think the max range it will go after a target is 100 yards, beyond that it won't listen and will just stay by your side/stuck on the pipe (this is why if it gets up on the pipe it won't go down after blackfuse) assuming you tank blackfuse by the other belt. Basically it means you need to send your pet at blackfuse soon after you jump down from the belt or get yanked off, because if you run to the pipe first you can be out of range. In order to do that you should manually resummon your pet as soon as you reach the main platform instead of waiting for the game to respawn it automatically, which takes quite a lot longer.