AI plan on using wilton black icing that comes in the tube tonight to decorate a cake. I've noticed that it seems a little thick and pulls away from the buttercream icing when I try to pipe the dots for a border.

I've thought maybe the buttercream on the cake needs to sit in the fridge a little longer to harden up prior to me piping...?? One other item I thought about was squeezing some of the icing out of the tube and adding water to thin it down..?? I wasn't sure if anyone else has had this problem and how you worked around it??

never bought tubes, or any kind of commercial icing for piping.  I've slapped a few tubs of chocolate frosting from the grocery store tubs in the old days - on undecorated cakes.  So can't say other than your thought to squeeze it out.  Actually I'd just cut the flat end off then put it in a bowl, mix in a tiny bit of  cream or milk - just a few drops at a time until it feels 'pipeable'. 

AYep I hardly ever use black so I buy the little tubes when I need some. Squeeze it into a bowl and thin it with some water and then pipe it.