What the F^cK is a T&P Valve?

So I went out to the garage to complete work on the engine from my beloved 95 4-Runner
after a 4 month hiatus(Head Gasket issues with complications)...

....when I discovered water all over the garage floor in various stages of pooling and puddling.

Ummm...what's going on here?

So I went over to the water heater for a closer look...and discovered water coming out of a long tube running down the side of the thing. 

Above the tube is a valve coming out of the water heater...

...and above that valve was a sticker with a whole bunch of scary legal-ease that basically read..."blah blah blah, under penalty of law, blah blah pressure blah blah valve blah blah" and was of no use whatsoever.

So being the perfect geek, I went back to Google and typed the words "water heater pressure valve" and figured out what the problem was right away. 

THIS THING right here is the culprit, and it would appear as though it's worn out and leaking.

The Home Depot website was of new use (as if it ever is) but Lowes.com has them all ready to go and in stock. 

So I now know what I'll be doing tomorrow.  It'll take longer moving all the crap away from that corner of the garage in the freezin-assed cold, than it will to actually drain the heater, spin the leaking valve off, and screw a new one back on. .

I wonder if I'll be able to get my thoroughly too-hip son or my soon-to-be-Ex-Wife to aid me in any way whatsoever with clearing away all the crap around the heater...HA HA HA, I crack myself up with all of the wishful thinking I find myself doing in my old age. 

 -The Dickens