Sea Ray

Welcome to the forum.

Yes the waste tank has an internal level detection assembly screwed onto the top.

Those three small cylinders move up and down about an inch during normal operation to provide the indications for empty, half and full.

It is common for crud to prevent proper sensor float motion, causing the described symptoms.

On my 2000 380DA that sensor assembly was hard wired onto the boat wiring harness. I modified that so mine now has an inline connector, to permit easy disconnection and removal from the boat.

When I am cleaning the internal surfaces of my empty waste holding tank I also clean that level detection assembly, using a garden hose and forced up down movement to ensure there isn't any crud on the sliding surfaces.

One advantage to the waste tank interior walls being clean is that permits visual inspection of the waste level through the translucent tank walls.

Thanks wingless for the insight. Now I just have to shrink myself to get into the corner where it's all installed! If only the boat builders would consider that when designing their beautiful models from the outside...

A bigger boat is a good solution to better system access.

It appears that holding tank access is possible but very difficult on that SLX  270.

Note, on my 2000 380DA some service / repair operations require removal of unrelated components for proper access.

It may be that on the SLX 270 there is also a prop rod (like on my boat) that permits detaching the lift lead screw ram. If so, then careful usage of that prop rod would improve holding tank access. 

Also the coolant tank placement is also a detriment to holding tank access. Temporary relocation of the coolant tank (w/ the hoses remaining connected) would improve holding tank access.

After reading the horror stories of other boats with varying degrees of success in cleaning and re-animating internal sensors, I find the idea of moving to external capacitive sensors appealing. It would of course be ideal if such could be hooked up to the existing control panel rather than installing a complete parallel system.

I'd be interested to hear if anyone has managed to realize such a solution - achieving signal compatability for the indicator EMPTY/HALF/FULL.

Here is an article evaluating several options.

IMO the factory system is fine and restoration to normal operation is "easy". Mine is always 100% functional.

Please report on any updates.

Done some more research on external sensors that may hook up to the existing monitor. One is a set of 3 sensors, example supplier

https://mikroelectron.com/Product/XKC-Y25-NPN-Waterproof-Non-Contact-Liquid-Level-Sensor-Switch-Sign...

where each sends a signal at 12v (0v for no liquid sensed). This would align to the 3 wires from the reed sensors of the standard sensors in the tank. The only difference is that the latter just closes the circuit of the 12V LED on the panel back to -ve for each level.

The question now is whether the signal wire from the external sensor is compatible (circuit-wise) to light up the LED, and not blow any fuses. Any experts out there that can comment?

Here are the wiring diagrams and view of the control panel. The holding tank (D4A) has not been installed as noted above.

So, I worked through it and found the solution. The actual sensor I used is XKC-Y25-NPN. Here is a sketch of the wiring for info. It is in German but easily translated where needed.