Hey there, good to see you posting!

What you have is a "balance line" - it's supposed to keep the pump from running dry, if the water gets too low in the pool (long story short, they don't work well )

When I run into these, I make up a pipe to screw into the port in the skimmer that will be above the water level, then blow it out with a vac/ blower. While the vac is running, I plug the port in the pool, add some antifreeze and put an expandable rubber plug in the top of the pipe. If you need details on how to make one, I'll gladly tell you

Whoever plugs the in pool port WILL GET WET! It helps if the person blowing the lines 'backs off' a little once it starts bubbling (maintain an airflow, but not full strength).