Can't fill water tank

Had my camper for 12 years and this is first time this problem has occurred.

Water tank almost empty. Put the hose in the fill hole and turn it on to moderate flow. Less than a minute later, water comes out around the hose, like the tank is full. Pull the hose out and water shoots out about 2 ft in 2 bursts. Can hear gurgling sound from fill hole for a few seconds after that.

Tried shooting stream of water into vent hole, but doesn't fix problem.

Any ideas?

Thanks,