Tell us about yourself!
You don't know what you are doing, most toilet cisterns use for the incoming water supply lead solder on the copper pipe, so it wouldn't be a good idea to use this for drinking or washing your hands.
I would recommend to insulate the tank.
You can get big problems with that and then you account will be blocked, and it is a lot better to just copy the CMD from C:/Windows and then rename it, BUT there's are/is a file(s) for the CMD that you can be admin, but I will not tell you that.
dumbass the raspberry pi has a smaller version of java pre-installed for minecraft Pi Edition so you can use that