A sleeping bag will eventually need a cleaning. How do you proceed, in particular according to the different materials?
The procedure is roughly the same for both Down and Synthetic, however down requires special precautions:
Sadly, despite being as careful as possible, washed down almost never seems to be as good as new. So do it only when necessary - if ever. Smelly bags can often improve just by laying out in the sun for a few hours. UV is brutal on funk-bugs.
PROTIP: Using a sleeping bag liner (silk or other) that will intercept your body's dirt and oils (the down-killers) will extend the life or your bag.
First of all, check the label for directions.
I have a synthetic bag. I take it to the laundromat and wash it in a sufficiently large front-load machine, using cold water and somewhat less detergent than a normal load. I put it in a large dryer set to low or no heat until it seems mostly dry. Then I hang it up indoors for a day or two to finish drying. This seems to be pretty effective.