From the
Pump Adapter Manual for 41094
Use with aqualis reservoir
Seal the lateral G ¼ connection thread of the pump adapter's
reservoir-facing side with one of the supplied sealing screws, the
central thread remains open. Use light force to slide the
connection ports of the reservoir base plate into the
corresponding receptacles of the pump adapter. Base part of
the reservoir and pump adapter should now be flush with each
other. Do not use excessive force and check for correct
alignment if necessary! Use four countersunk screws M4 x 12
mm supplied with the reservoir to fasten the reservoir to the
pump adapter. Use light force only in order not to damage the
threads in the plastic base part!
Connect the return line to the central connector of the pump
adapter (engraved “in”) and connect the other line to the lateral
connector (engraved “out”). Use light force only when screwing
in fittings in order not to damage the threads in the plastic base
part!
The way I read that is to leave the center hole on the pump adapter top open (path between reservoir & pump in) and close the off-center hole with an included plug, and then mount the reservoir.
To connect to your system, use the IN port on the pump adapter side for your return line (feeds center connection between pump in & reservoir) and connect the OUT port to the supply line back to the system (radiator?).
Good luck.