mould lines on hoses

Solid styrene or something flexible like vinyl? 

If it's styrene then slow and patient scraping and sanding. There are no shortcuts.

If it's vinyl, then you're pretty much out of luck.

It is a pain, just takes patience. It pretty much takes what you would think.

A good set of small needle files is useful too.

GMorrison

A good set of small needle files is useful too.

My first thought was needle files. I have this set from MicroMark and were it me, I'd reach for the kit and find a file that matched the contour of the ribs.

These are small files, about 5" long, 1/8" stem. Good luck with your hoses.

Make hoses from wire wrapped around a mandrel of suitable diameter.  Saves you the aggravation of micro-filing.

Ditto on the guitar strings. Find a place that gives lessons. They usualy have strings in the trash can that they'll give you for nothing. That's how I get mine.

Jim  

Late to the party but you might try dabbing Tamiya or Testors brand liquid cement on the ribs. 

The LC works by dissolving plastic so it might make the ridge flatten down. 

Disclaimer: this is only an idea, I’ve not actually tried it on this particular problem yet. Proceed with caution. 

Straycat1911

Disclaimer: this is only an idea, I’ve not actually tried it on this particular problem yet. Proceed with caution.

I actually have done it, numerous times. Works even better with a light brushing with an old toothbrush or soft-brass-bristles brush parallel with the corrugations. Like anything else, it's sort of a developed knack; practice on a non-critical part first.

I second the suggestion to replace them if possible with hoses made of wire.

This is an issue with Maschinen Krieger kits-it's a sci-fi genre featuring armored fighting suits.  Most of them have hoses in various places, and the kit-supplied hoses are in a soft plastic.  MaK modelers replace them with guitar strings, as noted in other posts; with fine springs; or by using wire or solder as a core and wrapping it with fine wire.  I use that technique.  I use wire solder, which is pliable enough to bend to shape, but will hold the shape I give it.  I wrap this with fine wire sold for beading crafts.  I can use my usual primer and paints on these hoses.

I'm another for guitar strings. Having 9 guitars and a bass...I have no shortage of old strings in all sizes.