Man i swear, this minigame and the discussion one is such a skill filter, just fill up the 2 first, it takes some time then fill sumpIf I remember right I did it more or less the following way.
Raise Pressure to max or near max
Wait until fullness goes to about 90%
Watch out that overpressure does not reach 100%
release the pressure and fill the sump.
Then repeat until sump is full then do the final push and fill overpreasure.
In the beginning you can drop fullness way down when stage raises the level of fullness you have to keep raises as well.
Be careful when you drop the fullness overpressure also drops a bit, try to keep it near 90% or it might be hard to get it up to 100% when sump is full.
Also dont blow her up.