Personally i just purge my oil through the quick couplers. Run the machine at idle and pump it out till it starts to spit. Shut it off straight away then replace the filter and fill with oil. You will need to top it off a few times till the bubbles all get out to get the oil level right. Some say its a bad idea as the pump runs dry, but there is always residue and i have never had an issue. Its your call if you do it this way or not.
The issue you have now may be air in the system from attaching the splitter. If you keep running the machine, it will self purge in time. If there is a lot in there it will naturally take longer.