Hey CP, They look just fine! It doesn't take a lot of concrete to sink PVC like it does for wood. Next time try using 18 quart plastic dishpans from the dollar store or Wal-Mart. I think that you will like them better than the buckets and they are reusable.
You don't have to drill any holes in your pipes. If you are not sure just try to pull one of them out after they have dried.