09-04-2019 09:51 - edited 09-04-2019 09:52
If the hose and fittings on the motor are installed securely and correctly, the only things that could dislodge them are a hose-fitting with too small an inner diameter (3/8" or less) that would push the outlet nozzle out of place when you screw it into the flushing port or too much water pressure.
You may want a technician to double check the engine plumbing and inspect things.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.