An apparatus may include a plunger and a substantially cylindrical body. The substantially cylindrical body may include an end portion having rounded edges and may define a cavity sized to receive the plunger. The substantially cylindrical body may include at least one opening extending from the cavity to an external surface. The at least one opening may a substantially irregular shape. In some embodiments, the at least one opening may extend from the cavity through a nub to the external surface. The nub may have a rounded shape. In some embodiments, the substantially irregular shape may include one of a slit, an oval shape, an elliptical shape, an hourglass shape, a rectangular shape, and a diamond shape. In some embodiments, the opening may be part of a non-cylindrical fluid passage.
