First off, if this guy is fixing anything on a ca: tell him to step away from the car. Soap does not, never did or never will stop a leak. Plugs stop leaks and tire sealant either will stop it or slow it down but may not permanently stop it, it all depends on the type of leak. Some sealants can corrode a wheel so you have to check what's in the sealant before using them. If he was talking about mounting a tire onto a wheel then that is a different story. We use tire seal which is a black sealant to coat the rim of the tire to help in mounting and seal very minor imperfections on the tire or wheel itself. Most of the time tire guys don't use it because it cost 12.00 a gallon, so they use soap because it's cheaper. Some guys will even use oil which is the worst thing to use as is any oil base product.