An apparatus includes a rigid body, a flexible sealing element, a nozzle assembly, and an electrode. The rigid body defines a channel, a reservoir, and a vent path. The reservoir is in fluid communication with the channel. The vent path is in fluid communication with the reservoir. The reservoir is configured to provide spacing between the channel and the vent path. The sealing element is positioned distal to the rigid body. The nozzle assembly includes a nozzle head and a post. The post extends distally through the channel of the rigid body. The nozzle head projects distally from a distal end of the post. The electrode is disposed within the channel of the rigid body. The reservoir extends laterally from a longitudinal axis defined by the electrode.
