Frostdamaged showers?

We have a small campsite with four showers. Even though mains was drained during heavy freeze, the showers were not individually drained. when they are now turned on the water comes out of the plastic tube which I guess lets the air in, located behind where the shower hose exits. On dismantling a shower, there are no blockages, but there is a small plastic washer which covers the exit whole of the plasstic pipe which has a 2mm hole / split in it. Is this the problem?