I have a small countertop dishwasher beside my pile of dirty dishes and the quick release that the dishwasher uses is by great luck the exact same as the quick release on my tank filling hose.
Buy a dishwasher and tell the wife that it is to make her life easier, then use the quick release in conjunction with your hose and fill that tank up with little risk. (the only risk is that she realizes that the dishwasher purchase was a premeditated trick to get at that downstairs tap)
this is the trick i used to get a quick release onto my kitchen sink. not quite a "countertop" unit, but a roll away unit cause my kitchen is strapped for space. (dishwasher in the hall closet for storage. lol)
with no shutoff at the bottom ,when you shut this system off upstairs ,all the water in the hose and pvc will still end up in the tank. hope you have some sort of overfill protection in mind.