Gulf Stream Prairie Schooner - washer drain pipe

[ivy9767]

Hi there! I'm so glad to find this site...this is my first 5th wheel...I live in it full time. It's been quite the learning experience. It's a 2007 38ft Prairie Schooner 5th Wheel. It has washer connections in the closet but the previous owners didn't have a washer they opted for the closet space. I purchased an RV washer, installed it...easy...then went to put the drain hose in and ran a cycle. The water came back up almost immediately. I put a coat hanger in to see if it was clogged and about 15 inches down it hit an obstruction. I can't see any doors or panels to open and view the pipes where the connections or drain pipe is. Does anyone know what is up with this? Is there a simple trick to it?

Thanks in advance.