What do they look like?
A black neoprene rubber sleeve with two stainless steel hose clamps (aka Fernco coupling)?
A stainless steel sleeve with rubber sleeve inside with torque screws (aka ho-bub or Mission coupling)?
If either, they're just couplings (not a check valve...wouldn't have anything like that in a vent).
Just tighten the screws. Should stop them from leaking.