Flash cooler line cleaning

[keghead]

Hello,

I am posting from Luxembourg, Europe.

I have recieved from my favourite bar an old flash cooler which I successfully fixed.

The problem is that this cooler was left unused in the bar's cellar for several years, and the guys from the brewery didn't bother emptying the lines when replacing it, meaning the beer stayed in the lines for years

The lines are in stainless steel so I'm sure they can still be cleaned some way, just I don't know what chemicals to use.

I have contacted a local brewery for cleaning products but they told me they don't sell these products to individuals for safety reasons. I was only able to obtain rubber balls from them.

I am planning to use the cooler very soon meaning I don't have enough time to order something online.

I was wondering if someone had an idea of chemicals/detergents I could use and available at the supermarket (Bleach ?) or chemicals I should never use as they could damage the line.

Thanks for your answers!

Note: it seems flash coolers are not common in the US. They are widely used here in Europe (we don't use cold plates or kegerators). The cooler I have is a 3-line cooler similar to the one below: