I am wondering if anyone uses a compressor or leaf blower to clean out ash from the barrel outward (duct work) or are cleanouts the best bet?

Blowing ash through the system from one end means that the ash will settle in any eddies in the ductwork (after elbows) and might ultimately build up enough to make a restriction. It might work in a simple system, if you can seal the blower end and any other openings very securely so as not to get ash leaking out. You still want cleanouts to be able to reach all parts of the system, just in case.

Thanks Glenn That makes good sense.I am planning on using 8" metal snap together HVAC pipe.Is there an easy way to make a cleanout at the 90's .The Y pipes are very expensive.

michael; There has not been enough ash in my rmh to get past my transition area, only 1/2 a five gal pail at the end of last season... but a shop vac with a long hose would remove the majority of any build up in the duct work.

Thanks Thomas,That gives me some pictures in my head on where to separate the duct work past the mass and then use a shop vac from two different directions to clean it out.The layout I have planned doesn't work out to well for cleanouts and this will work out much easier.Thanks again!