Is it okay to use a car wash water gun to clean the small heater water tank in a car?

First of all, the heater water tank is in the cab. If you want to flush it, you need to remove it first!

If you just flush the engine water tank outside, it is okay, but the premise is that the engine is cold. If it has just been started, it is recommended that you do not flush it immediately!

Also, during the flushing process, the water gun must be adjusted to mist, otherwise the radiator will be flushed up to the fins! Leading to poor heat dissipation performance!

I hope my answer can be helpful to you!