Haven't used the FW tank in the 5+ years we've had this TT. DW refuses to drink water out of the tank even if we were to use it. Only had a low pressure problem in a CG once otherwise city water has always had good pressure.
We've had the toilet valve fail several times (valve replaced twice) and one time water ended up on the floor and got into the insulation below. Pulled the coroplast down immediately and replaced the insulation. Not fun. The junk Thetford toilet has been replaced with a much better Dometic 310.
Since we never dry camp, I installed a 120 volt solenoid valve and a switch next to the door. If we go out, we just have to flip the switch and then don't have to worry about water damage. I think there's a water sensor that you can place on a floor to sense leaks and could be connected to a solenoid valve.
I even thought of installing a solenoid valve just for the toilet and a time delay off switch in the bathroom. Toilets are the most likely thing to leak. Someone could easily forget to fully shut off a sink or shower faucet and that could be a good argument for leaving grey tank valves open in a CG.