Bleeding brakes with a vacuum pump?

[friscobob]

I replaced the flexible brake lines front and rear(81 C10 SWB), used a hand powered vacuum pump to bleed them. Worked fine on the rear, got a steady clear stream of brake fluid. Fronts was a different story, got a steady stream of large air bubbles. So bleed them with a "hose in a jar" method, worked fine. I'm thinking since the front brakes work off the rear of the master cylinder that using a vacuum pump it just pulled air right past the MC seal, but using the hose the seal was under pressure and expanded and worked fine. Your thoughts?
PS I have manual brakes.