I regularly rinse the crud off of my Eheim canister filter pads under the running faucet, especially the coarse and prefilter ones, as they bear the brunt of the waste load. To clean the filter media itself (Substrat Pro, Ehfimech etc) I simply put it in a big colander and pour a large bucket or two of w/c old tank water through it, refill the baskets, and put it all back together again- and the quick disconnect hose assemblies make it very easy. Doing "poop scoops" in between w/c's also greatly cuts down the amount of waste getting into the canisters, as do sponge prefilters on the intake tubes, which can also be removed easily for rinsing.
Colin