The drain spigot works with simple rubber washers. A simple and light finger tighten is all that is needed to seal the bin. Over tightening can cause the inside washer to ‘roll off’ the sealing thread. By disassembling the spigot, you can fairly easily reposition the washer if it has rolled off. For opening half a turn is all that is needed to open the drain spigot. Over turning it can cause it to become unthreaded, and possibly remain in the ‘open’ position. If your spigot is draining by itself, then this is likely the scenario. Simply push in on the spigot handle while tightening, and the thread should re-engage itself properly.
Yours is very likely a result of over tightening, or over opening. Try the above and your problem should be rectified. If not, then the spigot can be fairly simply removed and repaired (from an empty bin). Just unthread the spigot from the nut that is on the inside of the bin, and open the spigot up (you’ll see the working parts). Then you can re-put the washers back in their original resting place, and the problem will be solved. The only tool you might need for this is a pair of pliers to hold the nut on the inside of the bin when you remove and reattach the spigot.
And as a reminder, all that is needed is a light half turn open and close with the spigot in the future and it should perform just fine.
Hope that helps!