How come it took mayweather so long to pee on 24/7

No you shouldn't be drinking a ton of water during a high intensity workout. It will KILL you! (water intoxication/overhydration)

Your body uses nerves to do everything. Your body is an electrical machine. Nerves are basically biological electrical connections. Water does NOT conduct electricity only electrolytes (salts) do. So if you drink too much water the electricity isn't conducted and you literally "ground out". Your heart can't beat, your lungs can't expand, and you DIE.

Now pushing it to this level is hard. Many people do it when they do something like a marathon, but you should NOT be drinking a ton of plain water when you work out. Drink pedialyte or gatorade diluted by half.

So Mayweather couldn't pee because he was training "dry" or at least "dryer" than most of us could probably stand. You should lose water and salt in equal proportions. Losing too much of either will KILL you.

 

or... he's cutting weight?