I pulled the carb and everything seems good to go with the floats.It will drain the tank if I dont shut off the fuel at the petcock.

If you get junk in the carb that doesn't allow the float to close completely it will over flow.

Float needle and seat could be bad...  float level could be a little high or kick stand bent so it leans over far enough to cause the overflow when parked.

Basic rule that has always been true on these old bikes is you MUST turn off the petcock when parked.  The original metal to metal needle and seat is not a perfect seal. 

Last thing I've seen is the brass overflow standpipe in the carb can get a hairline crack in it.  Rare, but does happen.  Would leak all the time though.

I just had the same issue, the float shaft had some visible corrosion on it so I cleaned it up with some steel wool. Had a stuck float, works perfect now.

I had the same problem, a grain of sand in the float valve.

Take the carb off & turn it upsidedown with bowl off & connected to the tank & see if the weight of the floats stops the flow or see how much pressure you need to add by finger to stop it. Then go looking for a reason if you can't stop it--or look for a reason if it 'is' easy to stop, a reason like floats touching something or set too high, or as been said a fault in the breather tube in the bowl. If its overflowing down the bowl breather then its likely some is getting into the motor as that breather is pretty high--'i think without looking'. Also i was thinking brass floats not those black ones on stalks. Brass ones can get holes in--unlikely but worth a look if that type.

The same thing has been happening occasionally with my CT3 too. Seems to be a sticky float; hitting the carb with the butt of a screwdriver seems to fix it in my case.