The Sabertooth has the "mix" built into itself, mixing hyd valves with hyd pump needs to be done through the radio programming.
Master will be the valve channel
Slave will be the pump
Put the pump esc on any switch ch, whether it be 2 or 3 pos.
Rate: will be +100% on one side and -100% on the other side
When programming the pump on whatever switch, make sure the pump is turning the correct direction to pressure up (not running in reverse). If you prefer the switch to be "UP" to be on & it's not, then go into the programming and REVERSE the channel.
A 2pos switch, one side is +100% & the other side is -100%. The correct direction to run the pump, on is 100% & off is 0%. Be sure to set the other side of "servo travel" in the radio programming to 0%
A 3pos will be +100%, 0%, -100%. Figure out the correction direction for the pump and make the reverse side of the switch 0%.
You never want the pump turning backwards, won't hurt anything mechanically, but might add air bubbles, then the system acts erractically for a short time till it self corrects.
I'm not familiar with the RDS8000 radio... does it have MIX within its programming?
That's the jist of what you need to do. Your manual will explain it in greater detail, but you will have to think in terms of an airplane (I don't fly either).
Spektrum is the best for construction models & programming!
Truckers like the RDS8000, wouldn't be difficult to trade up.