Each character's official weight is as unknown as their official ages, or the official layout of the lower levels of the shop.
As has been mentioned before, if we went with actual animal sizes, Doc would stand ten feet tall, Jinx would barely come up to his knee, Swampy would only be a little taller than that, and Jake would be about one-fifth Pirta's size.
Clearly none of that is the case, but then again, clearly they're not normal human proportions either, considering that Doc once ate an entire walrus, has been shown to be able to lift an entire car, and drink a five gallon bucket of "Monster energy drink" with few ill effects.
Besides, we know Doc doesn't have a "lethal" limit- once he gets past his "safe" limit, he goes into super speed mode. Even if he continued to drink Dew at that point, he'd burn it off faster than he could consume it. (Keeping in mind how relatively slowly it'd pour into his mouth at that speed- and how much would explode into spray considering he'd be trying to open a can that'd been shaken at 400Mhz the moment he picked it up. )