Fresh water tank plumbing question.

[sandy43]

I don't dry camp (till now) and really don't worry about the water tank. I've never been able to get more than 10-15 gallons in the tank before it comes back out the filler tube. I decided to play with it some more and again try to find the problem. I put 10 gal in with a little bleach to clean and sanitize the tank, let it sit for several hours, drained it good and repeated with 10 gal to get a good flush. This time I was going to leave the water in as much as I could in the tank. When it started to come back out the hole I removed the hose and it started to make lots of bubbling noise and water shot out of the air hose with a "burp" sound. What was that I thought. I then stuck the hose back in to see if it would take any more water. Wow, I added another 30-40 gallons. Was this some kind of an air-lock or possibly trash in the air hose? Has anyone experienced some close to what I described? I'd really like to know what caused this. Appreciate your remarks. Thanks
Sandy