This is how I build shocks without the need to use a shock pump, they travel flawlessly and rebound equally
1. completely empty out shock of course
2. fill shock body w/ oil only half way
3. move shock shaft up/down to transfer some oil UNDER the piston
4. wait 2 minutes or so until bubbles rise and pop
5. refill shock w/ oil fully but dont put too much... oil does not have to be level with the top of the shock body but make sure however much you use is equal w/ all 4 shocks
6. repeat step 4
7. put bladder on and screw shock cap making sure the bladder doesnt open up to get air in or lose oil
8. blast entire shock with motor spray to get rid of excess oil