Changing Hydraulic oil in Hustler Raptor SD 54

Hi, I am new to this forum and have a question that I hope one of you can answer. I have been doing maintenance and changing fluids on my Hustler so its ready when Spring rolls around. Today I was changing the oil in the hydraulic system and after draining it out putting new filters on I went to add the fresh fluid through the holding tank under the seat. I did this and filled it up a little past the cold level mark and noticed that it did not seem to be draining down into the transmissions, I then put the cap back on and cranked the mower thinking that might suck the fluid down, but it still remained at the same level. I then with the wheels off and the rear end jacked up pushed both bars forward and could see both hubs spinning, but still the fluid level had not moved as far as I could tell. I then took one of the filters off to check and see if the oil had made it that far and very little had. So my question is what is the procedure for refilling hydraulic oil in a Hustler Raptor SD? Thanks

Changing Hydraulic oil in Hustler Raptor SD 54