For quite some time I had been fighting a Model B carb leak from beneath the main jet, leaking past the drain plug on the bottom of the carb. I switched between a new brass plug and a new steel one with the same result: fuel collected on the bottom of the plug, stinking up the garage after a day or so. I lowered the float level and checked whether fuel was actually leaking out of the carb's air intake throat. It wasn't. The fuel was definitely getting past the drain plug. I think the problem centers around the threads in the carb itself. After years of use and hundreds of drain plug removals, followed by variations of tightenings, the threads are probably worn a little oversized so that fuel oozes past them. The plug can be tightened without any slop, but the fuel still is able to get past the gasket and plug threads. Using plumber's tape (the white plastic stuff) wrapped around the plug's threads will only work until the fuel breaks the material down and bits get caught in the main jet or further down the line. So, a tape was not the answer. No other commonly reached-for sealants stopped the dripping, either.
Finally, I went to a local NAPA store and asked about a fuel resistant sealer and was told Permatex Permashield sealant would work. It wasn't out on the floor with the other sealants. It was kept in the back for some reason. I bought a tube and took it home to test it. Before I applied it to the threads, I also replaced the drain plug's gasket that came with the carb rebuild kit. It seemed too hard to seal properly. I bought a softer material fiber gasket at local hardware store and slid that over the plug's threads. Once the threads were coated with this sticky non-hardening blue sealant, the drain plug was tightened and allowed to cure overnight. For the next few days I would start the engine, turn off the fuel and allow the engine to die. I checked the bottom of the drain plug each morning thereafter. No gas! I did this every day for a week and am glad to report that this sealant did the trick. Before, each morning there would be a little gas collected on the bottom of the plug. Not anymore!
If this experience helps the OP and others with a dripping carb, it was worth the $15.00 this stuff cost. But to have a garage without a gas smell is worth more than a measly 15 bucks to me!
Marshall