Just wanted to add my $0.02. To save a lot more than $0.02, a nice alternative to the Python No-Spill gravel cleaner is the
Lees Ultimate Gravel Vac (check
http/www.thatfishplace.com for pricing, etc. -- plenty of other stores carry the same product). It's about $15-$20 US dollars cheaper than the Python and it's basically identical and just as high in quality. You can buy them in 25-foot and 50-foot sizes, both kits include an adapter for the siphon intake that prevents you from sucking small fish into the intake. At any rate, these things do save you a ton of time and agony, and I highly recommend them for any tanks larger than 20 US gallons in size that could require several bucket trips for even a 15-20% water change.
As for the questions concerning dechlorination, just add the dechlorinator to your tank immediately before refilling it with the gravel vac. To match water temperature, use your finger and compare the water coming out of the faucet to the water in your tank -- your finger can gauge temperature to within a 1/2 degree (believe it or not), so this method should be fine. If you change less than 25% of the water, you don't need to worry about matching the water temp as much, but try to approximate it as best as possible with just your finger. I have a digital thermometer measuring my tank temperature and have never seen my tank temp change more than +/- 0.2 degrees F during a water change.
Also, pH in tap water is usually very close to 7.0 (neutral); obviously quality of tap water varies based on where you live. Unless you need a specific pH for breeding or whatever, you generally don't need to adjust the pH just because you added tap water. Whenever I change the water, I add some "stress coat", a dose of Cycle (to stimulate beneficial bacteria growth), and a dash of aquarium salt. I have gotten great results and have yet to experience water chemistry problems using the above methods.