Once construction is complete and the skimmer is introduced into the tank, initial start up is the critical moment to set up right, the mounting / lock screw keeps the unit at the right water depth, the open end of the "T" piece should be open to air inside the tank and well above the water level on the classic 100 HOB skimmer, keep the silencer well above the height of the foam level and never below the tank water level to avoid a disaster should the pump stop. Now the unit is running everyone thinks the foam should immediately rise up the collector tube and slowly overflow into the collector cup from the getgo - wrong. The correct position of the collector cup base should be positioned where the foam starts, resist pushing it down further as an overflow will occur at some point within a couple of hours and start to overflow. Avoid this mistake, setting the base of the collector cup so foam is just entering the bottom of the tube no more than 1/2" is perfect. Now be patient and let the unit break in and start to do its job, approx 3 weeks until fatty molecules start to thicken the foam up that will push it up the tube into the collection cup, this approach avoids the undesirable overflow when unattended. Give it time and don't push it, it will deliver the anticipated all in good time.
For such a nice piece of equipment, shame on the manufacturers for not being a responsible manufacturer and failing their customers by not supplying a proper installation, operation and maintenance manual with their equipment. Shame Shame Shame on them.