Flop tube for header tank

[Flying High]

Does anyone happen to know the size flop tube I need for my header tank in the S1? It's a Haigh header tank I think, similar to the Raven one but the plane was built before Raven was making these I believe.

Also, any tips on getting to it? I don't seem to have access via the firewall like some with S1 do.

 

[Flying High]

 

[nicko]

 

[Carlyle]