Bought one of those Sungrabbers for my brother in law. It does have the disc. Basically, it turns the 2 x 20 into a 1 X 40, the water goes in the input, goes up HALF the tubing to the other pipe, comes back down the other HALF and exits at the output. If you want to put more than one, it makes sense to bring and input to EACH panel (otherwise, if you go input->output->input->output, you are just creating a HUGE series panel and that is going to restrict your flow and make the panel less effiecient).