Clear Plastic Tubing and Funnels is a favorite apparatus. I try to set it up every year. I did not set it up last year, so it was the first apparatus I set up for our new school year.
The setup is as follows. There is a planter tray set inside the table that is the base for the apparatus. A crate is then duct taped to the tray to make it sturdy. Next, funnels are inserted into individual pieces of clear plastic tubing and the two are duct taped together. The tubing is threaded through the crate so the funnel sits on top of the crate and the tubing exits the crates in various places. The funnels are secured to the top of the crate with duct tape. The clear plastic tubing is also secured to the crate and various parts of the table to make them secure. In the picture above, the highlighted funnel is connected to the tubing that empties back into the table through a sprinkler head. What that means is that the water is poured into a funnel on one side of the table, crosses over to the other side of the table through the tube running through the crate, and travels along the opposite side of the table along the edge before emptying into the table through the sprinkler head.
Here is a picture showing where the other funnels that are connected to shorter tubes empty.
And if you go to the other side of the crate, there is a big black funnel that is connected to a black tube that empties into a second water table.
And when the children begin to figure out how the water flows through the "water machine," there is a lot of focused action that usually connects several children.