grey water draining very slowly

Sounds more like a vacuum issue - no air getting back to the tank to equalize - especially true if the gush happens every time. Rock the RV slightly or simply run some water into that grey tank (kitchen or shower) and see if the flow kicks right up again. If it does, its simply vacuum, if not, then look for buildup or vent plugs etc.

I sounds like you have something that is loose in your gray water tank that shifts during the draining process and plugs the hole.
I would not trust the gauges but you have to determine whether your gray tank is emptying completely. If you have a piece of debris in the tank, the only way to get it out is to try to fish it out with some type of hook to snag it.

First Comment is that the sensors are not trust worthy - mine are very inaccurate and have been since new.

Try closing the grey port and stick a use a hose pipe to fill the tank as much as possible. You'll know you're nearly full when the drain in the shower stops draining. Then open the grey tank valve and full drain the tank - try to tilt the camper so gravity is helping you out.

Otherwise, you can use a "plumbers snake" to come in through the valve (careful here - don't force anything);

Gerry

When they install the tanks, they use hole saws to create the inlet openings at the top and the outlet openings at the side /bottom. They rarely remove the disk created by the hole saw in the gray tank (they usually can fish out the black tank disk because it is a 4 inch opening). These disks can cause the water to run slow when they get near the drain opening. You may also have a vacuum build up if the vent is clogged. Here is a trick: When the gray tank stats running slow, open the black tank valve; this will vent the gray tank since the black tank was drained first and is empty.

If if shows completely full all the time sounds fishy your sensor is probably screwed up like most of them are. Why don't you dump the grey and see how many 5 gallon buckets of water you can pour down the shower drain. Then you will know if it is just a sensor issue.

My suggestion is to open the drain and leave it open until nothing is trickling out anymore. Close the drain. Go inside and run hot water in the sink until there is no more hot water in the water heater. You can supplement this with a good size pot of boiling or near boiling water from the stove. Wait 5-10 minutes and then open the drain again. Doing this a few times should melt off the grease that has built up in the tank and improve your flow. From here on make sure you wipe everything off with paper towels before putting it in the sink for washing.

It has happened every time. We're still pretty new to this coach, but that's about to change as DW is retiring Friday! I haven't tried tilting it yet, and one youtube video suggested pouring some liquid automatic dishwasher detergent in the drain to break up grease and crud. I'm going to try that, since we get an odor from the grey drain when it gets full. (odor comes from the shower drain) Thank y'all for the help