holding tank issues

[rckc2417]

I have a 99" 52cpmy. My 3/4 full light started coming on. I pulled the sender and cleaned it. When the sender was out I confirmed with a stick that the holding tank was empty. After three uses of a toilet the 3/4 full light comes on. I went down this morning and disconnected the vacuum line for the sender. there was a lot of pressure being released. any thoughts?
thanks

[jmooney]

Vent is clogged.

[rwaldrop13]

Vent or vent filter. I had to pull my vent filter to pump out my holding tank, but it took me a long time to figure out. At least you can stick your tank, I couldn't even do that. If you have a vent filter installed in your tank vent line, replace it or eliminate it.

[rckc2417]

I definitely have a plug in the fitting on the tank. trying to break it free now. I am going to see if CLR will loosen it. I tried a water blast no luck. thanks all for the assistance.

[rwaldrop13]

I definitely have a plug in the fitting on the tank. trying to break it free now. I am going to see if CLR will loosen it. I tried a water blast no luck. thanks all for the assistance.

If you can find it in your area, there's a "cleaning vinegar" that is a 30% vinegar solution. I'd try that first.

[rwaldrop13]

If you can find it in your area, there's a "cleaning vinegar" that is a 30% vinegar solution. I'd try that first.

Or the admiral suggested Rid-X, the septic tank enzymatic cleaner.

[jmooney]

Sew-clean .

[rwaldrop13]

I dumped this in my tanks on recommendation from another liveaboard in our marina, that like us, had holding tank issues. But in hindsight I think the 30% vinegar was more effective.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1