Hey, I use Speidel 12L, 20L, and 30L fermenters exclusively in my brewing, and I think they're pretty simple to keep clean...
When I'm done with one I give it a quick blast with hot water from the hose and dump all the gunk in. I then put in a scoop of my homemade PBW (about 3-4 tablespoons for the 30L and a less for the smaller ones), and I fill it all the way to the top with hot water and leave it to soak overnight.
While that's going on I just use a bit of PBW I've got pre-mixed in a spray bottle and a wash cloth with some hot water to clean the airlock, lid, etc.
The next day I go out and drain the fermenter through the spigot, using a wash cloth to touch up any spots that need it, but the PBW soak almost always gets the toughest stuff out, so that's rarely needed. Then I just rinse everything a few times, take off the spigot, and store it upside down to drain out.
To sanitize on brew day I usually just fill it with a 1/2 gallon or so of Star San solution and then shake it around a few times whenever I think about it. Then I drain that out right before I'm ready to drain my kettle to the fermenter and just fill on top of the little bit of foam remaining.
So far so good!