brake bleeding suction sound

[api1243]

my car is a Corrola RunX 2003 with a 3zz-fe engine
so i was switching my rear brake pads and rotors and decided to make a brake bleed on the way since for a while my brakes have been really soft..
while i was bleeding the rear left caliper first with the vaccum bleeder i ofcourse notices the greenish/black old fluid coming out and tons of bubbles like insane ammount almost no fluid compared to bubbles..
i was at this points almost 170ml drained and it became the clear new fluid but the bubbles still came out... i was doing a mix of pressing brakes and using the vaccum just to check for diffrences well everytime i pressed the brakes themself without the vaccum bleeder i can hear a suction sound as almost if brand new air is getting in the system.
i was bleeding 200ml when i removed the bleeder and just connected a clear tube to some random bottle i found out that pressing the brakes will extract only pure new brake fluid and no bubbles and it will go about 5 cms into the tube and will come back when i release the brakes so i was happy thinking the bubbles are out on this side but again i went to check for the noises (mind you i dont have an actual brake fluid leak.. i have been running 2 years without doing anything related to the fluid and it stayed on the same level)
so again with the random tube and bottle connected and pressing the brakes i can hear those noises right where the 6 brake lines meet near the abs about the corner of the engine bay but in the tube it self even 3-4 presses no bubbles... i decided to make a switch again for the vaccum bleeder and the second i connect it and pump it its again sucking tons of bubbles like nothing changed and even more on faster rate as if the new fluid helps it move easier.... i was frustrated and said lets continue for now and went to the rear right caliper and the same thing ... i bleeded until its looking brand new thinking the air will go away and with the bottle+tube combo it shows as if nothing is there but connecting the vaccum shows just how much there is there as if its just getting brand new supply of air from that suction sound i hear...
i decided to stop since at this point i have wasted about 700ml of brand new fluid which is starting to be pricey for something that didnt really helped me sure the rear has new fluid now but air is still there and i am not sure if i should keep on going bleed the 2 front calipers or diagnose it...

[TonyHSD]

Hi, for brake bleeding best the old school method with help from a friend to pump up and hold the pedal while you undo the nipple and bleed. 

[Derek.w]

Your vaccuum unit is pulling the air in go the way TonyHSD reccomends thats the way I prefer or you can buy new brake nipples add a ring of locking compound around the threads when its dry change it over with the one you want to bleed. The sealant ring helps to stop the air entering when you crack it open.

(Note leave reservor cap on when chainging nipple over remove for bleeding wheel)

[APS]

Don't use suction. You might just be sucking in air around the nipple. If you have the correct adapter then press air into the main reservoir. Otherwise use the tried and tested, manual method as Tony mentioned.