Hello all,
just did this yesterday while removing my siren. I did remove the cowl. There are one driver, one center, two passenger separated by a little rubber flap.
I used a shop vacuum and reduced the hose size to 1/2 in and ran it in there got a lot of interesting plant matter out.
then I used solid stream on a water hose sprayer and sprayed a little stronger each time till ran without restraint.
I also had a camel pack hose brush about two feet long and ran it through till clean.
Hope this helped.