There is too much potential for sucking back air through a one way bleed pipe to convince me it is a reliable method. If the fit of the pipe on the nipple is poor, air will be drawn back. If the thread on the nipple is worn, air will be drawn back. If the check valve is sticky, air will be drawn back.
The only reliable manual bleed method I know of is a two man operation in which one presses the pedal while other wields a spanner on the nipple. In essence: fit a hose to the nipple with the lower end in a clear glass jar, loosen the nipple, press the pedal to the floor and hold it there, tighten the nipple, release the pedal, top up the reservoir. Repeat until air bubbles can no longer be seen emerging from the hose. The spanner man controls the process and commands the other when to raise and lower the pedal using clear orders like "up" and "down", which the pedal man repeats when he has carried out the order.
There are various pressure and suction systems available which can automate the process, but having never used any of them I can not comment on their effectiveness.
You are rightly concentrating on getting the air out, but have you considered that the spongy pedal may be caused by defective seals in one of the cylinders?