[Desert185]

I made an air to water adapter for blowing out the system rather than using the adapter with a "valve stem" where you have to hold the air hose on it.

Male 3/4 hose brass fitting to 1/2 NPT male.

1/2 NPT female to 1/4 NPT female brass coupler.

1/4 NPT male air fitting (I use the industrial, brass version).

Screw it all together with teflon tape, attaching a water pressure regulator to the hose end.

Screw the water pressure regulator into the trailer's city water port.

Attach air hose (air pressure now doesn't matter, but I still turn it down to 40-50 PSI).

Turn on air and open faucets one at a time, near to far sequence, including flushing toilet and outside shower.

Attach to black tank flush and blow that out.

Simplifies the process.

Edit: all this sfter draining the HW heater and bypassing it.