The check ball is either dirty or off seated causing water to by-pass and come out of the tube. In some instances when the chemical hose has not been activated for a while there is a chance that water may back-feed through the chemical hose.

Here are the steps to go through to fix the problem:

Place the hose in a bucket of water.

After starting the unit, place your wand on low pressure.

Allow chemical hose to siphon water.

This should alleviate the problem.