Seamless pattern help

[astrophoto]

Hi all, I have been using PS for around 10 - 15 years, so I know my way around a little, but not a pro. I have a problem which I hope I can describe in such a way that is easy to understand.
OK, I have a job to do where I need to design hydro graphic film. I need to design a tile with a complex design but it has to match on all sides (square) and repeated so it can be printed to the film up to 50 meters.
I understand the pattern tool and using the offset filter, but I need it to loose the lines so it perfectly flows.

Any idea's would be very welcome.

Thanks in advance

Steve

 

[SCTRWD]

I often use 3D->New Tiled Painting for this task.

Make a new layer with your pattern. Then go to 3D->New Tiled Painting. You'll see your pattern tiled on a 3x3 grid.
Make sure you have "Paint on" option in a 3D panel set to Diffuse texture.
Now use Clone or any painting tool to draw anywhere on your 3D layer and the tiles will update automatically to reflect your changes.
When you are done just open the Diffuse texture and save it as a pattern.