Neutral territory is your first step. Out on the lawn in an enclosure, in a room they've never been in before, in an empty bathtub lined with clean blankets etc. Anywhere that doesn't smell of either piggy. Pop both the pigs together in the neutral area.
Nipping, chasing, butt-sniffing, mounting, rumblestrutting and nose-offs (sniffing each others noses then lifting them up quickly as high as they can) are normal dominance behaviours. These behaviours will always be around as a daily part of your pigs' lives, but they will be more intense when they first meet each other.
What could indicate an imminent fight is snorting, lunging and yawning (showing teeth). Always have a towel to hand when giving introductions in case you need to separate the pigs from a ball-of-fur fight - pig bites can be very nasty if you don't protect yourself. Throwing a towel over them confuses them, so they stop fighting, give you a chance to check them over, and if necessary separate them. Remember only separate if there is bloodshed. If the pigs do get into a ball-of-fur fight, then separate them momentarily and re-introduce them on another clean blanket in a new area.
If absolutely nothing works and they continually get into ball-of-fur fighting then a 'buddy bath' may be performed, where you bathe each pigs' butt and shampoo away their scents. Once they have dried off then they will smell the same. If you feel brave enough then bathe the pigs together (after all, this is the point of a buddy bath), and they should be so terrified of what's going on that they will forget about fighting and will bond with each other through fear.
Once you are happy that they have startinggetting along, clean the cage out really thoroughly. Everything which will be in with the pigs must be clean and not smell of any piggy - it has the potential to undo all their hard work in the neutral territory.
