PVC isn't rated for air though. Due to it's properties it can shatter into sharpnel and the reason OSHA won't allow it for air lines in shops. If the potato gets stuck or something else happens the pipe can explode like a hand grenade. Just something we're trying to make you aware of.
1/4" ID tubing will really restrict the volume, and more volume is what Don was hinting at for you. If you don't have anything bigger than 1/4" (I imagine you are using the same SMC polyurethane tubing we got in the KOP) and you don't want to buy anything bigger then try adding several feeds of the 1/4" tubing to your gun. This will help the tanks discharge faster which equals greater volume.
