I would use a exhaust hood spinner for the inside. That way you can close the door and blast away without getting any crap on you. LOL
That actually is not a bad idea if they had a good size opening in the top!
Most of the ones here are plastic like what the tanks are made out of, not too many of the one-piece fiberglass units like from years ago. The new ones come in flat boxes and are just panels that you connect together then add the top and then secure to the bottom, the high winds here blow them over all the time because they are not heavy like the older ones were.
Get a good brand graffiti remover and with a long wand and attachment (pivoting nozzle holder that Russ at Southside Equipment sells) you can get just about anywhere without getting the crap all over you then sanitize it.
Look at the MaxQuat that Delco Sells, it does a great job and leaves a "medicine" kind of smell behind which might be preferable over bleach on hot days. hahahahahahaha
I used that MaxQuat on a job the other week where I sanitized after cleaning up bird nests (6 large hefty bags worth) and a lot of bird droppings and that stuff got rid of the bird dropping smell real good.
The customer was happy and that is what matters!
I might look into the crapper cleaning business! hahahahaha
That just sounds too funny but might be a good source of income in these times, you just never know.