It didn't work?!
This is a flawless technique, you must've done something wrong Perhaps even accidentally letting water out without realising it, when you were doing up the bolts.
Make sure to only have one hole uncovered at once.
Having the pads on under water makes no difference to the quality of the bleed.
You can bleed a brake with a syringe, and hosing, but you also need a barbed fitting so you can attach it to the slave cylinder bleed hole. You might be able to use part of an old crossover, though, but you need a syringe that actually fits it.