I have a brand new 2016 Fatboy S and have noticed that all the oil in the oil tank drains into crankcase within 2 days of being parked. On start up, it takes 5 seconds for oil pressure light to go out and the oil is pumped back into the tank. It has only done 4500km. The leak down seems to be getting worse. 
From what I read, the oil draining into the crankcase past the georotor oil pump is normal for a softail when it is parked for a few weeks or more.
I have talked to the local HD dealer and he confirms it will leak oil from the tank into the crankcase, but doing it within a day seems to be unusual. He is going to write to HD to ask if it is normal for the tank to empty in a day.
The bike is still under warrantee and even if they say it is normal, I don't buy it. My wife's brand new 2016 Fatboy S, same kms, shows slight drop on the dipstick, even after sitting for a couple of weeks, where my oiltank would be completely empty.  
Has anyboy else experienced such a rapid leak down with their Softails? and would a new oil pump be the solution?
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its the return check ball valve letting it leak back through the oil pump, easy fix

I wish it was that easy. The Twin Cam engines since 2000 did away with the check ball valve mechanism. Now there is no check ball valve. According to the manual- The oil pump is a geroter style consiting of two pumps, one for the scavenge side and one for the engine. I would say mine is out of tolerance hence it is leaking down so quickly. Oil pressure light goes off after about 5 seconds, so I am assuming oil,pressure is okay.
The manual says to do a preride check and the oil should be between the min and max marks. Then run the bike to operating temperature and recheck the oil level and fill to max mark.
The HD mechanic is going to send HD an email and ask if it is an issue if after two days the tank is empty. I would say there is. My wife's bike, same model, same kms, the oil drops a little 1/8" even after not being ridden for a month. Mine would be bone dry after 2 days.
I think HD need to pull the pump and replace. The bike is still under warrentee. Tomorrow I will go back to the dealer and see if they have had a response.
Thanks for your reply.

The dealer did some research with HD and says the wavy spring washer that sits between the two plates with the gerotors on either side is faulty. He says the strength of this wavy spring washer controls the leak down. So my ride is booked in at the end of the month to get the faulty spring washer replaced and he will also check whether the gerotors are within tolerance and replace as necessary. Also says no dowels are needed to align the oil pump on the 2016 models.
I am pleased with this result.