Out of interest, how were you intending on filling a 400L tank from a first floor flat?
I don't but used to.
I had a 650 L tank in the van then.
I'd spurred off my mains with a washing machine tap to a 4040 ro mounted high on the wall in my hallway .
I'd fed waste and pure pipes under my floor boards. Waste went out a hole I drilled in rear wall and in to gutter down pipe.
Pure re emerged in living room and went through a hole i drilled in wooden window frame and was zip tied to a gutter that lead to the ground floor front door and porch with a hoselock tap on the end.
When I needed to make pure I would have to persevere and try and get a parking spot close enough to my front door to connect up about 20 meters of hose, this could often take a couple of hours of an evening in itself. It would then take me about 3hrs to fill from empty in which time I would sit near the window keeping an eye on things.
This went on for about 7 years until before xmas just gone when I thought f*** this ! and started buying water off a window cleaning friend of mine.
Happy days

and I got my life back !
