Is the system designed to work in the opposite way than your description?
I wish it was a two way system. I say this because when I brought the boat from FL to SC one of the days I was not aboard, the captain I hired did the transfer....probably because he was concerned about running out of fuel, which is because the fuel gauge doesn't work ! (send unit really...another tale of woe...)
The next day I get back aboard and notice the boat is listing ever so slightly...which most people would not even notice but drives me nuts because it was dead level when I bought it. I eventually noticed that the aux tank is off center in the construction drawings of the boat. So almost certainly that is why it's now listing...it's missing the weight of the fuel in that off center tank.
Why don't I just go get some fuel and fix that situation ? Well...that's another story...
Anyhoo, the fuel transfer toggle seems to have 3 positions so I wonder if it could transfer the other direction. But the "transfer" light only comes on when I flip it all the way up...so I suspect it's small tank to large tank only. Apparently serving as an emergency source of fuel.
But I don't
really know for sure, thus this topic....
While the Viking manual shows the tank in the drawings, there is zero mention of it, or the transfer system anywhere in the literature...not the capacity, nothing...