Create a pattern in 'Shop and you can copy/paste it into the clean. Trim away the excess with the Polygonal Lasso tool and then redraw anything that needs to be on top of the pattern. Line art, clouds, etc.
Denoisers are a 3rd party plugin for photoshop, they aren't included with it, a lot of scanlators use it pretty frequently, and a lot of them are really bad at it too. Their VERY easy to over use and instantly make a page look like garbage.
As for getting them. I recommend Topaz DeNoise3. You'll have to look at getting it yourself, as it costs money and I'm pretty sure I can't tell you to go pirate something on the forums.
And as for using it, on Topaz DeNoise 3, make sure the page is in RGB mode, then the 2 main settings to play with are suppress noise and recover detail, and every manga and raw have different needs of those settings. I typically use it before levelling the raw, but their are other methods out there.
the diagonal pattern is the same as in the raw. it wasn't tilted. the densoising process detect the original pattern and try to restore it to that state. but i wouldn't call that perfect. the grey isn't uniform as in you can see the darker spots in the middle.