A couple of things we did on our new L400.
There were no bilge pump alarms
The pump switch is activated by a water sensor, not a float
waste goes to a manifold that is connected to the bilge pump as well and also has a non return valve inline
The problem is some water can flow through the non return valve into the bilge when using the shower. This soapy water can film over the sensor and stop it sensing correctly.
Also I like clean dry bilges so if there is ever any water I can diagnose where it has come from quickly.
Fit bilge pump alarms directly to sensor
Remove manifold and run shower wastes directly to additional dedicated through hull
Reliable system so far
The other day the water heater pressure release valve released some water. It's the second time it's done it. Maybe 5l of water. It happened around about the same time our water tanks
ran dry so maybe something to do with that, but the point is I was able to notice and find the problem within 5 mins, which wouldn't have happened if the original system was in place. Also met a L450 owner that had his alarms going off shortly after showers. I assumed it was a similar system but Dave are you saying the water is somehow following the shower head
hose from the shower down into the bilge because it's not sealed correctly?