An apparatus includes an elongate shaft, a dilation balloon, and a fitting member. The elongate shaft includes an inflation lumen, an irrigation lumen, and at least one irrigation opening. The at least one irrigation opening is in fluid communication with the irrigation lumen. The dilation balloon is at the distal portion of the shaft. The dilation balloon is in fluid communication with the inflation lumen. The fitting member is at the proximal end of the shaft. The fitting member includes an inflation fluid port, an irrigation fluid port, and a blocking structure. The inflation fluid port is in fluid communication with the inflation lumen. The irrigation fluid port is in fluid communication with the irrigation lumen. The blocking structure is adjacent to the irrigation fluid port and defines a gap around the irrigation fluid port.