There are a lot of issues with deep end main drains. Usually you can't blow them completely because of the pressure required. Yes, to blow lines volume is required, not pressure. I can see where a high pressure compressor can be used for the main drain line to lower the water in the pipe below the frost line, then plug it or throw a valve. On your return lines...how deep are the return jets? Mine are at most 14" below water level and either my shop-vac or my electric leaf blower will work. Used both. At most a gas powered blower should be much more than enough.