I would be wary of doing that, although it would probably work if you were super-careful to go very slowly. The idea behind siphoning it in to a vac port is to get just a little at a time in there. Pouring too much at once could lead to hydrolocking the engine, in theory.

Seafoam makes a spray called Deep Creep that I would feel more comfortable using down a carb throat.

John B.