The one-piece flo-jets have a rubber ring set into a groove in the carburetor body. The top of the float bowl bears against the ring. Here is what it looks like:
http://www.ereplacementparts.com/gasketfloat-bowl-p-358912.htmlWhether a hole works as a drain depends on factors such as whether it is clear, and whether it is at the low point. The latter aspect may depend on whether the engine is tilted, for example. If the engine turns over freely, the piston rings have not rusted onto the cylinder bore. This is very good news.
