Skid steer hydraulics reservoir...too much air?

Before I get into my concern, hope everyone had a great Thanksgiving. Bought a post pounder to run off NH L223 skid steer. Post pounder requires a hydraulic hose to "dump" fluid back to the hydraulic reservoir. The fill tube has couple ninety degree bends which only allow hose to go in so far. So each time the pounder slammed down on the post I would loose fluid coming out of fill tube. So pounding post on the first day was a short day. I think I might have a solution by plumbing in a flexible coupler and male 3/4 inch to female connector mated to a 3/4 inch female pvc cap (there is a 3/4 inch threaded hole in middle of cap). The cap is attached to other end of coupler and other end of coupler is attached to fill tube. The dump hose is attached to 3/4 inch coupler. So now the fluid should be contained. Ok, now the question. Should I be concerned as a certain amount of hydraulic fluid is spewed back to the reservoir as the hammer drops is the reservoir building up any pressure? Fluid is displacing air in the tank but the air has know where to go. Anyone come across similar issue?

Skid steer hydraulics reservoir...too much air?