Board Thread:Questions and Answers/@comment-5961239-20130107010351/@comment-4787191-20130112113101

If that's a filter connected to the deployer, it is taking out empty buckets, but also not letting lava buckets in. Hook the pneumatic tubes directly up to the deployer and have the filter take out empty buckets. Alternatly, you could have an advanced wooden transport pipe to take out buckets and put them back in the ender chest