I use a 60/40 Multicore with water soluble flux that way I can wash it off with water and make the joint clean. Kester also makes a water soluble flux solder as well. The key is a hot iron, especially on something large. I also use a Metcal soldering station, don't remember the wattage (it's about the size of a 30W iron), but I can do 10 gauge easily and I can solder together a roll of pennies with it so it does the job.
When I am at home I use the same solder, but if I have to to large wire I use a 250W gun or my portasol for smaller items.
Using a flux pen works wonders when doing large gauge wire, I also use one that is water soluble. I'll have to check the brand.
Jeff
The Warnings & Cautions discussed in this manual cant cover all possible conditions/situations. It must be understood that common sense and caution are factors which cant be built into this product.