If the pedal slowly continues to sink while you're holding it, it is because fluid is escaping the pressurized part of the system at some point. If it's not a master cylinder seal that it leaking, you will lose fluid. The hoses will pressurize immediately, and thus won't cause a sinking pedal. They may cause increased pedal travel, in which get them off your car immediately (but I doubt that this is your problem).
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