I've seen them in all sorts of positions including at the bottom, mainly to clear the chassis.
I have a bit of flat bar same thickness as rotor. Take off caliper and fit flat bar between pads, hold caliper so screw is at the top, and bleed.
Recommend these guys if you need a tank/tanks
https://www.kiwitanks.co.nz/caravan-water-tanks
And these guys for bits and pieces
https://www.rvworldstore.co.nz/