Losing prime when tank is 1/3 full

[Jman9599]

Hello everyone,
First post here. I have a 2021 3033BH, when fresh water tank gets to 1/3 full I lose prime. I then used 5 gallon buckets and opened up the drain valve. I captured about 15 gallons still left in tank. Sensor now reads empty. So basically I can't access about 15 gallons of water. Has anybody had any issues with winnebago water tanks like this? If so how did you solve it. My guess is line suction is above 1/3 and would need to be relocated to bottom of tank. Is it tank sag?

Thanks everyone.

[DavidM]

The suction fitting on most RV water tanks leaves maybe 10% unusable, but never 1/3. Take a look at the plumbing from the water pump back to the tank outlet. Maybe it is kinked (like mine was) and as a result won't pick up the last 10-15 gallons.

David

[Jman9599]

Thanks David will check it out appreciate the response.