How to drain the float bowls
A light-hearted overview
1. Grab a screwdriver (3mm Allen or flat-tipped, depending on bike age)
2. Get a Coke can
3. Find a Ginsu Steak Knife
4. Use the Ginsu knife to cut the Coke can 1/3 of the way from the bottom. Discard the top.
5. Stick the can bottom under one carb
6. Locate the brass screw under the bottom of the carb
7. The screw is actually a tap
8. Turn the tap to drain the float bowl
9. Hopefully you turned the screw on the carb above the Coke can. Otherwise, your engine is covered in gasoline
10. Repeat for other carb
When you're ready to ride again: Turn the petcock to PRI (prime - if you have it) or ON and crank the engine. It'll take several seconds and feel like eternity to get enough gas into the carbs so the bike can start.
This one isn't quite so sarcastic, but it has good pictures
First off, the bike under dissection here is a Bandit 400. While not a 250, the work is the same, things look very much the same, and you'd get the same results (meaning this is something that is bike/manufacturer independent... the only requirement is that there are carbs).
Tools needed (in this case) are a phillips #2 screwdriver, a glass jar, and a hose/funnel. The 250 would need a 3mm allen instead of a phillips #2 screwdriver.
In this next picture, the large screwdriver is pointing to the drain screw. It's always facing one side of the bike (not down, or up or forward... )
This photo shows the drain nipple, where the gas actually comes out.
The kind of shiny strip in this photo is just a channel of tin-foil used to direct the gas into the glass jar. Normal procedure uses some hose, but you can make do with what you have, should all your hose have been discarded in a recent move and you don't feel like taking a trip to an auto parts store. Anyway, you just open (counter clockwise, lefty loosey) the drain screw, and fuel will drain out the nipple. You DO want to make sure that the tank petcock is turned off (if there is an off), clamped, or the vacuum system is working, or else you'll drain fuel from the tank, through the carbs, until the tank is empty. Pretty simple:
Here's the jar of gas... yes, 10 oz. came out of the carbs (Note: 4-carb system - YMMV). It's that dark green because the previous owner didn't drain them and the gas sat in the carbs long enough that the corroding brass jets turned the gas this dark green. Not a carb-cleaning to look forward to.
And finally, some clean water was added to the gas so you can see the separation. Normally, when you get water in the gas at a station it's this dark, dirty, murky, nasty looking water... very much NOT clean like this. But if you have any water in the float bowls, it can cause poor running or no running at all.
To refill the carbs when you're ready to ride again, just turn the petcock to PRI (prime - if you have it) or ON and crank the engine for a while. If you're just cranking the engine, it'll take several seconds (feels like eternity) for the fuel to drain into the float bowls and get to the level where it can be drawn into the engine.
And that's really all there is to it. Make sure to dispose of the gas in a safe, environmentally friendly manner.