Small Engines (Lawn Mowers, etc.): detergent tank overflow, detergent tank, honda gcv 160

Question
John, thanks for your time.  I have a Honda GCV 160 5.5hp pressure washer that runs great, however the water line that supplies the detergent tank sprays under high pressure as well and overflows the tank when in use.  

I suspect that there is a check valve or something thats inop.  If so how do I fix and where is it located?

Am I on track or missing the problem all together?

Answer
 Hello David:

 Send me the Model Numbers Off of the Pressure Washer, Please. The Engine Numbers are for Engine Related Problems Only. I think you are Right as that is what is Most Commonly the Cause of this Problem. However, I would Prefer to Look at the Pressure Washer Diagram and Be Sure. Thanks

 Respectfully

 John