An apparatus is provided for permitting a substantially continuous flow of drywall compound to a wallboard joint. The apparatus includes a delivery tube for delivering drywall compound completely therethrough. The delivery tube has a first end connected to a drywall compound supply assembly fed directly by a source of pressurized drywall compound. The delivery tube also has a second end opposite the first end in communication with a drywall compound dispensing head. A normally closed, pressure sensitive valve arrangement is interposed between the second end of the delivery tube and the dispensing head for controlling the starting and stopping of drywall compound flow between the delivery tube and the dispensing head.