I've worked on literally hundreds of different self-serve washes. There is not "usually" an injector. The most common way for
soap to get to the pump is that there's one tank with (typically hot) water and another tank with mixed
soap. The hot water feeds the pump straight and a solenoid between the
soap tank and the pump controls the flow of
soap when needed.
QUOTE]
Perhaps by saying injector I used the wrong word.
Your explanation above is lacking as well.
There is a solenoid between the
soap tank and pump, but somewhere there is a line from that solenoid that has to "T" into the supply where the
soap is injected into the supply for the pump. when the solenoid opens the
soap gets sucked into the pump along with the plain water. But there needs to be som mechanism for keeping any
soap left between the solenoid and pump from backing up into the plain water.