Hi Mandy, It sounds like to me that your 1/4 reading may be a phantom reading that is moisture and not liquid. Not that unusual on an older coach. If you have access to the side of the fresh water tank where the wires attach to the probes, you could replace the 1/4 location with a new "well nut" next to it. A well nut is a rubber sleeve with a stainless steel 10-32 bolt and nut, washer assembly. After you drill a 3/8" hole with a "step drill" you push the well nut into the hole and as you tighten the bolt the rubber expands to seal the hole. remove the nut and install the original wire. You can purchase well nuts at an RV parts department for about $6.00.
On my coach when the tank says 20%, shortly thereafter the pump won't shut off. Fred