pilot light on gas water tank goes out.

: the pilot light on my gas water tank keeps going out. : It might stay on for 1, 2 or maybe even 3 days, but : then goes out again. When I relight the pilot, there : is no problem, until later that day or in the evening maybe.. : I replaced the thermocouple, but it did not help. : Are there high output thermocouples? Could this be the problem? It usually goes out in the morning or at : night, sometimes it seems that when we use up all : the hot water, the pilot goes out. p.s the pilot light : does not seem that big when lit, but the gas is opened up all the way. This just started happining the last 2 weeks. Baffling because when I light the pilot, it : does stay on with no problems. I dont think its an updraft because i have another tank attached to : the same chimney, and I have no problem with that : tank.Yes, I understand, because Im having the almost the same problem with my gas furnace–which is a hot water boiler system. I, too, have replaced the thermocouple. Now I need to know how the pilot light should look when properly adjusted. Like, should there be any yellow at the top of the blue flame?? If so, how much (yellow)?? None at all?? A 1/16th of an inch?? An 1/8th of an inch? A quarter inch?? I have turned the adjustment screw that is supposed to set the height of the pilot light, but the dumb flame looks exactly the same no matter how much I turn the adjustment screw in either direction! Help!!