I searched the archives but I still don't feel comfortable after changing my hydro oil today. Here is the sequence I followed after reading the Great Dane coloring book manual. -Made sure everything was clean. -Removed reservoir top and filter. -Disconnected line from each pump and drained. -Disconnected line between each pump and drained. -Loosely re-connected each line. -Filled new filter, 15w50 mobil 1, and attached. -Filled reservoir. -Disconnected each line from above and re-connected after flow started. (bleeding procedure) -Raised wheels and ran in forward for 1 minute and reverse for 1 minute. -Checked reservoir and added 15w50 until full. It seems to be running good with no hydro noise. I just want to make sure I don't ruin a pump. How do I know if air is in the system and how do I get rid if it ? Thanks.