Build a water mortar

Step 8 Install end plug

Work the end cap into the end of the inner pipe. The head of the bolt should be visible. Once it is started you can turn the pipe over and tap it against the floor to seat the plug tightly. If the plug is not tight enough it will get sucked out when you draw water into the chamber. You can use a wrap of electrical tape at the base of the plug to make it fit more snugly.