don't use a wire brush on stainless unless it's specifically made for stainless steel. as you should know, stainless is much harder than mild steel, so when you use a regular old welding brush on stainless, you're leaving mild steel fragments in the stainless. ..which is what's rusting. if I'm...
the only problem with welding stainless steel with regular wire is the weld won't entirely be stainless. The two metals blend forming a sort of alloy and unless treated it will rust. I work with stainless steel creating art pieces and I weld it with mild wire.
I wouldn't weld a sink with...