question as above

Yes, but you need the right flux and the SS tarnishes very quickly if the heat is kept on.

Yes, but it will be brazing rather than soldering. You need brazing rods with a high silver content and an oxygen-acetlene flame.

Yes you can solder them (just checked). They need to be clean and you need additional flux. Multi-core solder by itself isn’t so keen to wet the surface.

You can also silver solder* it (which is known as silver brazing by some).

*Solder with say 1% silver in it aint silver solder though. That’s just solder with a bit of silver in it. Silver-solder has 40-50% silver and you need something that chucks out more heat than a soldering iron to melt it.

FYI I used Fry powerflow flux and standard 60/40 multi-core solder.
If you’re talking about silver-soldering then I use Tenacity No 5. flux.

Ceeway are good for lugs and frame building supplies inc brazing / silversolder and fluxes

I buy my silver solder from
http://www.cupalloys.co.uk

Thanks its not a critical part. just a bit of 10mm stainless pipe into a 10mm to 15 mm copper reducer
it wont by used under pressure just gravity

MAPP should be adequate for what you need, rather than acetylene. My propane torch takes a MAPP cylinder. You can buy MAPP gas and brazing rods from B&Q etc. Try not to get the stainless any hotter than necessary for any longer than necessary or it may lose its stainless properties.

Alternatively, if the joint isn’t going to get hot in use, I would use araldite or similar epoxy.