Dead Volume (Belly?) in AC Drain Line

I own a 1964 house in Austin TX. If I use a compressor to blow out the AC drain to completely empty, then I pour in water at the top, it takes about 2.5 pints before water starts to come out of the drain. In a perfect world that polyethylene pipe would be set up with a continuous slope, and no water would accumulate at all, right? Is this much of a belly ok? Is it normal or typical? Thanks! BTW there is a proper p-trap setup at the condenser. I'm talking about downstream from that.

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