Brake issue after rebuild

[Kingkitesurf]

A very strange thing occurs with my completely rebuild brakes. Everything is new. New master, new booster, new lines, new pistons, new 4 pot front upgrade, new bottles, new fluid. After bleeding the lines with a pressure bottle system (1.2 Bar) and parallel using a vacuum suction system on the bleeder end there still seems air in the system. First press is deeper then the second one. After the second push I am trying to hold pressure and it very very slowly keeps dropping. I did not start the car (so maybe no vacuum activation yet)…
Checked all connections and lines but no leaking.
As there was almost 1 liter of brake fluid in the vacuum canister before rebuild I suspect the valve on the vacuum canister could be faulty?
What else can this be? Faulty new part like master cylinder?

[Tom W]

Are you sure there’s no air in the system? What fluid are you using?

[dal2.0litrefrogeye]

Hi so if I'm reading this right with your foot on the pedal pushing down , it will slowly sink to the floor ? ......... sounds like your new master cylinder is letting by ,