Put an adapter on your faucet in the house. You can buy them at hardware stores. Unsrew the piece on the spigot, srew on the adapter, screw the hose to that and adjust water temp.
Just add water very very slow...Never EVER add hot water..For many reasons...It leads so seam failure, oxy deprivation, and just throws off a fishes systems...Too many to list. Hot water heaters have horrible bacteria in them, and also the pipes are copper...I would kill my rays if I used hot water, and many other people make this fatal mistake everyday. As long as the tank has a heater, just fill it with all cold very slow..I try to feed way less in the winter to match the lowered amount of water changes my fish recieve...In the summer time it is rainy season in my house for my fish..hahaha Good luck.
Unless you change massive amounts of water it's not and unless your water comes out near freezing or you are making extreme water changes the temp difference should not cause any real problems.
I do what Duke33 said. I put a thermometer at the end of the hose to check the temp as it goes in the sink then close the valve on the hose and drag the hose to the tank and open the valve on hose. They sell them at most lfs I think. Thats where I got mine years ago. Can't remember last time I used a bucket for a water change. Just to top off.
$5 shower addapter (they are on a peg near the toilet seats) from homedepot and a $2 adapter (in the pvc section) to turn it into a hosebib = $7 for full temp control of your water..
the best part it you can leave it in place.. no need to change fittings everytime you do a waterchange
So easy to do....I bought a hose just for inside the house use, as in doing WC's for my three tanks. The adaptor is inexpensive and easy to install. Years ago, I used 5 gallon water bottles that I filled from the tub.....you get a good workout but it gets a little old fast doing tanks larger than 125G.