normally about 5 scoops to 15 - 20 litres of water.
I heat up the racks as hot as possible in the oven, fill a tank with very hot water & powerburst, then just drop all the racks and removable fittings in the tank.
Leave them while i clean the rest of the oven which is also hot so good gloves are essential
By the time ive finished most of the grease and carbon just slides off, a quick going over with a scourer, and jobs done.
Not really sure why people buy expensive dip tanks and burners etc, i've never needed them in 15 years, i always clean them like this, takes normally 1.5 hours.
Cant say I enjoy doing it, but its all money
steve