Sea Ray

Welcome to the forum.

Here is the L 590 FLY Owner's Manual.

The Vacuflush system is very straightforward. A few basics, don't flush anything except approved toilet paper, or something passing through the human body.

The starting point is to verify an empty holding tank. Note that the level sensors can get stuck, so don't depend on the indicator panel. On my 2000 380DA, I periodically unscrew the level indicator (that I have modified from hard wired to now having an inline connector) to permit "easy" access to pumped out empty waste tank, to permit scrubbing the interior w/ a looong brush and powdered cleaner. I also clean the level indicators at the time. Back and forth movement w/ a garden hose and a small brush ensure those work properly.

Beyond that, a likely issue might be a clog in the hose between the head and the vacuum generator. My process is to keep the flush lever depressed after solid waste until I hear the audible change from pumping to empty plumbing. I have found that method to be 100% successful.

If the hose is clogged, then unfortunately a plunger can be problematic. The vacuum generator uses four duckbill Joker valves to generate the vacuum suction that pulls the waste into the tank. A back / forth plunger motion can invert that rubber duckbill valve, then game over.

Over time the duckbill Joker valve rubber gets hard and replacement is required. Do NOT excessively tighten the fitting when replacing as it will deform the lip seal, causing a small leak and unacceptable idle usage pump cycling. The fittings only need to be snug.

In my case I have successfully used a plunger multiple times to clear a hose blockage. In my case I turn off and bleed pressure from the fresh water DC pump, to prevent overflow when attempting to clear the clog. I ensure a full bowl of water. Then I used the plunger only for the push stroke and tip to the side to break the seal so no suction stroke. I always keep a plunger onboard just in case.

There is a Platypus forum that instead advocates for the most disgusting job on the planet, breaking apart the full / sealed waste hoses on a failed Vacuflush system and using digits to pick poo and pons. That is not for me, but on the plus side, they award a commemorative tee shirt to all those who follow that advise.