The way I interpret this is if you have the Ultra-Lube axles it means you have a grease zerk on the outer end of the axle, which I believe most all Voltages have. The way this works as I understand is, like Tanman said, when you pump grease into the zerk it comes out behind the inner bearing and if your seals are good it forces the old grease in the inner bearing back into the space between the two bearings and then back through the outer bearing, forcing all the old grease out to the end of the axle. You pump until you have all new grease coming out. This will probably take more than a tube of grease on each axle and a lot of rags to clean up the mess. The factory does not pump the center of your hubs full but when I cleaned and repacked mine last fall, all the bearings had plenty of grease and were good, which is how I prefer to do it instead of pumping the hubs full. I did hand pack some grease into the center of the hubs but not anywhere full. Also my seals were bad and 3 of the 4 brakes had grease in them. That probably happened when I pumped some grease into the zerks and it went straight into the brakes. Just my take on it anyway.
2015 Harley Road Glide Ultra CVO
2020 F-350 6.7 SRW SupurDuty Crew FX4 Lariat