Real generally speaking, running ~225-250 on an 18.5 WSM...what is the ballpark amount of time I could expect a full gallon of water in the pan to last before requiring additional water (assuming I don't want the water to run dry)? I've been reading a lot of heat sink/water/no-water threads - don't want to go there here - I just can't find how long a full pan will last for a typical low and slow smoke. Thanks