1996 Windstar windshield wiper vaccum

My wife didnt like the type of windshield wiper fluid that I put in the van so she bought a new gallon of the "blue" stuff.
She decided to drain the old fluid out by just keep pressing the button until the old fluid was out ,then I would just add the new fluid.
Well I put the new fluid in this morning and it took the whole gallon, which tells me that she really drained the whole tank!!
Well now when I push the button for the fluid to come out it seems as if it wont catch,the fluid light comes on and it dings like its empty.
Is there something special that I need to do to prime it,or do I just keep pushing the button until it catches?
The reason I ask is because I dont want to burn the motor out,because the motor is still working just fine I can hear it pumping.

What can I do ?

If you have a self bleeder like a vacuum pump for brakes will work but if not you can do it the old way. Find were it plugs in at may be hard to get to on the windstar at the washer nozzle and you can siffon by mouth.I have held a hose pipe in the filler with pressure and it would swirt through the nozzle on its own. That may be the easier of the two.
My wife has ran our van dry many of times but never had this problem.It took a long time for it to reach the back window though.

Could be that the pump inlet got plugged with stuff that normally was floating around when the liquid level got low. I'd try removing the pump and cleaning.