Ok so I figured out a work around.
I set the max on time for the return pump to 0, and used programmable logic to get it to do what I want.

The only downside is there is no alarm to warn me when my top-off container is empty.

On another note, the computer software it displays 12:00:00AM for Max. on-time. (Probes/sensor controls -> Level 1)
I'm assuming this is just a bug?