This is my first real issue with the boat. When I bought it, it was surveyed. There were no reports of issues with the shower drains. I have used the master stateroom shower and it drains fine. Last wknd I used the hall shower and it did not drain. The Carver ops manual refers to an 'optional gray water tank'. I do not have a gray water tank.

Section two discusses the sump pump, and operation with a 'breaker' to enable:

2.2.1.2 Auto Sump - Forward and Aft
This breaker controls the flow of electricity to the forward and aft sump
pumps. Because the sumps are located below the boat’s water line, the
sump pumps are needed to pump shower waste water, sink waste water
and air conditioning condensation overboard or into the optional grey
water tank. Each sump pump is activated automatically by a float switch
whenever water within the sump rises above a predetermined level.
Switch the Auto Sump - Forward circuit breaker “ON” before using the
air conditioning or showers and sinks in the port and starboard heads.
Switch the Auto Sump - Aft circuit breaker “ON” before using the optional
crew quarters’ air conditioning, shower or sink.

Well, I don't have a 'auto sump' breaker anywhere on my DC panel either. I know the drain for the sinks is working as they drain well. When it was surveyed, I don't think they ran the shower enough to have the auto float switch. Which leads to these questions:

1. Does anyone know where this sump pump breaker is supposed to be on the DC panel? I don't have it listed.
2. Does anyone know where the tank and pump and switch are located in the engine bay so it can be tested/fixed?
3. I KNOW not to use a plunger on the vacu-flush as it will invert the flapper of the valve. Can I use a plunger on the shower drain in case there's a blockage?

The hall way bathroom sink seems to drain just fine. I would presume they go to the same tank, so I'm fairly sure I have a blockage in the shower to tank section. Any assist would be appreciated.