First, I've never cleaned your grill, so decide on your own if any of this is a good idea but here's how i've cleaned mine:

I've breathed new life into my grill with a pressure washer. Pulling the grates off and putting them on the ground then spraying the bejesus out of them with a pressure washer. Should work on the outside of the grill too.

I've also had good luck getting cruft off with barkeeper's friend. It should be fine for anything enameled or stainless steel. I'm not sure how you clean the sear burner.

I remember looking at their grills when I bought mine. As I recall, everything is stainless with a few exceptions. So I would suggest:

Remove the grates and put them into your oven on self-clean, if they'll fit. Else try EasyOff, the stuff intended for use when cold. Rinse thoroughly.

The fire bricks will clean themselves once you get it hot, but you could use a stiff brush on them to clean them off.

Once you get every thing out of the inside, spray washing (like you would for a car) should be sufficient. You can use something like Dawn to cut grease. Be careful with using any metal scrubbers since they will scratch the stainless.

If it has electronic ignitors, then try not to get them wet (the battery pack and such).

I used to use a steam cleaner back in the dark ages, it worked wonders on car chassis and old engines maybe it'll get the grease off your grill.

As long as you wash/rinse the parts thoroughly afterwards, there are any number of automotive degreasing products you can get...just find that isle in your local auto shop. Use that in conjuction with a pressure washer...just watch out where you spray all the gunk and the cleaner - its not really the type of stuff that should go down the drain unless you choose some of the enviro/citrus cleaners.
Caspian

With car products, you're talking about petroleum based grease. This is animal fats, so the dishwashing soap may be better. And more environmentally friendly.

There are companies that clean ovens. Maybe they also clean grills. Sounds like you could use a professional cleaning. I believe Trevor Lawson at eurostoves told me about professional oven cleaning places - maybe contact him and ask.

I'm with SeaKoz and use a pressure washer every three years whether it needs it or not. I took the grates out and blasted them on the ground and then hit everything inside as well. If you don't have a pressure washer then I think I might try the easy off approach on a warm day, but only for a half hour and wash off with a hose. I think it might damage the stainless. If the grates are coated then you could leave them longer.

the 304 will scratch, so keep that in mind when you do the outside. DON'T get the power washer near the infrared burner as you will crack it.

Mads (the OP) posted on another forum that he/she already cleaned the grill. Mads forgot to inform us that the buildup was actually carbon, not grease, which presents a totally different cleaning challenge. A photo would have helped a lot here.

Mads cleaned off the carbon buildup with a cup brush in a grinder.

Billy

To protect your burners I would apply duct tape while doing any pressure washing. A carful spay with Gunk engine clean will add a foam with stoddard solvent or other paint thinner type of component. Srpay heavily and just let it stand for an hour, then respray and use pressure wash to strip away grease. I think that can work but be sure to protect burners and igniters first.

Hey Everybody!
I know the lot of you haven't been able to sleep over this so I thought I'd fill you in.

First off, as usual, I was saying one thing and meaning another.

The grill was really, really, greasy.
A soaking in straight simple green and a green scotchbrite pad cleaned up all the grease quite nicely.
The outide of the grill looks like new (many envious manly men types at the bbq yesterday).

What I meant to be saying all along is that the CARBON build-up is what I'm trying to clean off. The three day soak in simple green didn't do anything to it.
I'm talking a 1/4" thick layer of hard baked on carbon on the the grates, the burners on everything inside the grill.
Just like the top of a piston in an old V-8...

Someone earlier suggested a grinder...well, I took your advice.
I was able to acquire a cup brush with brass bristles for my 4.5" angle grinder.
With the angle grinder I was able to clean off the grates, the burners, the inside of the grill pretty darn well.
All the grates and burners came out looking almost like new, just a little blued from the heat. I actually wore the brush out almost completely...and I still have some more to go.

The grill worked pretty well, not sold on the smoker feature. It just made a LOT of smoke for about an hour and then burned out. Love the two sear burners, they were handy for cooking the marinated chix breasts.
this big grill does suck through a lot of propane and towards the end I had to switch tanks out because one was icing up and I lost pressure.
All in all, $400 well spent I think.

Mads

Easy Off oven cleaner

soak your wood chips before putting into the smoker tray. You could also put a layer of water in there enough to cover the bottom. Some will put herbs or 'aromatic liquids' (ie, beer) in this tray as well.

EasyOff would clean this. Spray washing is fine but I forgot to mention to remove the ceramics and the burners before washing out the inside.

Carbon on the burners with burn off (same as the ceramics) when it gets hot enough.

I want to suggest a propane torch. Carbon burns. Try burning off the carbon on an inconspicuous place. If it works there keep moving.

Great - but don't put the filthy grates, etc into your oven inside!
The smoke would set off your smoke detectors!

Mostly, I just run my grill for a time period to allow it to burn off. If bad enough, I scrape the sides down

I do have a super Weber brush that is pretty darn good.