Connection to antifreeze supply

[Top2MP]

I have a 2015 Thor FourWinds 22E. I have located the bypass valves and the port where the antifreeze is supposed to be added. My question is what type of connection do I use to connect the siphon hose to that port?

[Beau388]

On my coach the fitting is a female 1/4" -27 national pipe thread (NPT). I use a male air coupler plug. That is the fitting at the end of an air hose. I use to blowout the water lines with my air compressor then attach a 1/4" siphon hose and jug and flush out the pump with antifreeze.

[Top2MP]

I have attached three photos of the setup for adding antifreeze for the Four Winds. The blue circle shows the cap on the antifreeze fill location. The red line is where I measured the diameter at approximately 5/8". The third photo shows how it is connected to the pump and also the valve that closes the water draw from the water tanks I just noticed the photo is on its side and should be rotated clockwise 90 degrees). I have not been able to find a fitting for a siphon hose that would work here. Anyone have ideas?
Thanks, Top