Alde water problem

i just drove 200 odd miles to a new campsite. It has 50 amp service only, which ive never used, so i usef the dogbone connector. I hooked upelectric and wayer and took the dog for a walk to return to a motor noise and water flowing from under the trailer. I turned off the water and it stopped.  No water inside, none anywhere under the seats, around the Alde drains inside. But from the evidence under the trailer it appears to have been coming from the yellow flap outlet. Why? What happened? I thought something might have shaken loose. The Alde was and still is off, by the way.