Step 7: Now for the professional water rockets
This stage of the instructable will show you how to make a big one stager and how to couple or splice bottles together.
step 1 : coupling and splicing
How to couple bottles
first drill a hole about 7-8mm in width in the bottom of one of your bottles.
Next screw the male end of a plumbing coupling which is about 8mm in width into the bottom of the bottle, then seal it with a sealent glue. Next drill an 8mm hole in the other bottle cap and then insert the male end in to it. Whist the bottle cap is off the bottle, screw the female end into the other side of the bottle cap (side facing the inside) If you want you can seal it with glue as well.