Cut hole to the hole saw size for your Uniseal.
Ensure that the hole is clean with no sharp edges. Irregularities can cause a poor seal and leaks.
Insert the Uniseal into the hole with the wide flange on the outside of the container.
Ensure the pipe end that will be inserted is clean of burs or sharp points. File the edges if needed.
Insert the pipe into the Uniseal. You can lubricate the pipe end with Windex. Most of it will be squeezed off during installation but be sure to wash thoroughly before turning on your system.
Demonstration of the Uniseal attachment from Bulk Reef Supply.