You can clean the mechanical and chemical filtration media with tap water. You just want to clean the biological media with tank water so chlorine from tap water wont kill off any of your beneficial bacteria.
For me, the water still left in the canister filter is enough for me to rinse the biomedia with. It gets clean/dislodged enough. If thats not enough, just use a cup or something to scoop some water out of the tank for more tank water to rinse your media. Less work and cheaper than rigging up a new valve with tubing.
You could actually just set a bucket below the tank and take some airline tubing, put one end in the tank water and the other in the bucket, suck on the end that goes to the bucket to start the siphon and let that siphon the tank water to the bucket, simple and its actually pretty fast at siphoning.