A gas delivery system for a processing chamber includes a first channel for delivering a first chemistry and a second channel for delivering a second chemistry. The first channel includes a first outlet valve and the second channel includes a second outlet valve. A trickle gas source is connected to both the first and the second channels. A first junction is coupled to the first outlet valve and a second junction is connected to the second outlet valve. A common conduit connects between the first junction and the second junction. The first junction includes an input to provide a push gas from a push gas source and the second junction includes an output to a processing chamber. During operation, one of the first channel or the second channel is active at one time. A trickle gas from a trickle gas source is flowed into an active one and a non-active one of the first or second channels. A push inert gas from the push gas source is flowed into the first junction, through the common conduit and out of the second junction to the processing chamber.