A locking sealing arrangement for providing a fluid tight seal between a cap or a spigot and an adjacent structure is set forth. The locking sealing cap includes a peripheral sealing member such as an o-ring to form the fluid tight seal. The locking sealing cap engages the inner surface of the adjacent support structure by a cam-lock arrangement. A locking tab extends from the surface of the support structure. A tab-receiving slot is formed in the locking sealing cap. Once the locking tab is aligned in the tab-receiving slot, rotational movement of the locking sealing cap causes engagement of the locking sealing cap with the support structure. One embodiment of the locking sealing cap includes an internal torque feature for receiving a tool to allow engagement. In another embodiment of the locking sealing cap an external, multi-sided tool engagement surface is provided.