Well... ... I don't like to disagree with upstanding members like Bill Fleming, but I can't find the darn thing:-{} I was at the NorCal Diesel Rally in Napa, CA this past weekend, and a 12 valve member blew his water pump and I helped him change it. His engine had ~180K miles, run pretty hard. He blew it after doing a monstrous burnout contest and blowing one of his tires
Anyway, I actually had printed out the page you will find at the link Bill provided above, and took it to the rally in the hopes that someone there could help me find the darn weep hole on my truck, as I have never been able to. After seeing where it is on the 12 valve pump, even though the 12 and 24 valve water pumps are very slightly different, it at least gave me an idea where to look... ... 4 of us spent almost a full hour looking on my truck, and another 24 valve truck, looking from the top, bottom, every possible angle, and we could absolutely not find or even feel it!
But, the good news is, the pump takes about 5 minutes to change. Remove the serp belt, 2 easy bolts, and you're changed. By the way, Greg got a new one for his truck at a local Napa, I think he said it cost like $60. Whole thing fits in the palm of your hand. It sure ain't like no water pump I've ever seen before.
Tom