Kitchen sink & toilet clogged

[skmille]

When draining the black & grey tanks only a small amount came out of each. Both the sink & toilet are now stopped up to the point you can see water in the pipe in the toilet when the toilet is open & water is backed up in the kitchen sink, also there is a drip coming from the underbelly of my 2020 keystone cougar 5th wheel. HELP

 

[Fish]

Sounds like your dump valves aren't opening. I can't imagine something being large enough to clog your outlet that much.
It's a little early for it to be froze up.

 

[docj]

I've read about relatively new RVs where "cutouts" for connections to the black and gray tanks were dropped into the tanks and eventually became pressed against the tank's outlet. I'm not saying that's what's happened to yours but it's possible.

One course of action would be to use this device to "gently" force some water back into the tank. I say gently because you already have water backed up inside the RV. FlushKing
I have one and use it primarily when soap and food particle residues clog the relatively narrow drain to my gray tank. Fortunately, I've never had such a problem with my black tank but we're experienced RVers.

Of course, if the dump valves aren't opening, that alone would be the cause of your problems.