Fill the trough with water add caustic soda.Make sure you use rubber gloves,wash the fingers & all the rubbish will be gone.
slide out the frame which holds the belt,take outside spray with oven cleaner let it sit for 15mins & hose off.
If it is just the belt which is grubby turn the timer down to 1.5mins get some steel wool &run the steel wool backwoods & forwards along the belt & presto,one shiny new looking belt.
Hope that helps you out
Johno