I tried bleach with minimal effect, I then went with drain unblocker but no effect. I didn't want to put an air hose or water hose down the drain in case I blew off a joint in some inaccessible place under the floor. Today I bit the bullet, engaged contortionist mode and started trying to trace the waste pipe. After sponging the last of the cocktail from the shower tray and removing an aluminium panel / floor support I found this,
What you're looking at is the waste from the shower coming in from the left to the center of the pump and exiting to the waste tank. the white thing in the center of the second picture is a solenoid which is activated when the pump comes on. Presumably it's there to stop any water flowing back from the waste tank into the shower tray. A daft idea in my opinion especially as it's reducing from 1" down to less than 1/2". Does anyone know if this is a normal set up for 2002 Hobby 600 and if so what switches the pump on ? Perhaps a pump is needed as the shower tray is so low but why cause such a restriction in the pipe ? Any ideas welcome.