Why do I empty my bladder more on some days than others?

Dear Matt:

Sometimes on a cross-country trip I can whiz right by five rest stops without "resting," and at other times I barely make it from one stop to the next without taking a leak. And that's with no variables in coffee consumption. Same goes at home. Occasionally I find myself emptying my bladder at 20-minute intervals after a single beer. The next day I'll down two or three and go for hours without a flush. What gives?

-- Barry, Encinitas

The office quack, Dr. Doctor, sez these plumbing questions can get tricky. And since Dr. Doctor is a drywall hanger, not a real doctor, he and his attorney suggest you stop getting medical advice through the mail and spend a few bucks on a real M.D. if this "gottapee!gottapee!" problem gets worse. There are several unpleasant things that might cause it. But since he's a drywall hanger, not a doctor, he won't go into that now. He'll take the easy road.

We pee when a fancy nerve bundle in our bladders signals our cranial whiz center that things are getting full. What squirts into our bladders is what's left after our bodies have used what they need for other things. So if you're sweating heavily one day, you'll make fewer bathroom trips. But maybe your problem isn't #1, it's #2. Your bladder is like an uninflated balloon when it's empty. If something's pushing on it (like a full colon), it gets "full"er faster, ergo, more need for that annoying "resting."