RC Tanker
Allows you to drain an oxygen or water tank then use it to fill another tank.
It works with elevators/lander rockets.
Adds two buttons to the selection panel: One to switch between draining and filling, and one to switch between oxygen/water (will empty tank of current resource).
By default it can hold an unlimited amount, includes a mod option to limit it to X units (if you feel it’s too cheap).
Depending on DLC installed RC and tank will use different models.