It seems that most states have rules against the transport of antlers/bones unless *cleaned* before transporting across state lines nowadays.

The easiest way to stay within these laws would be, best I can tell, to debone all meat and 'clean' all skulls/teeth (like elk ivories) before bringing them home.

How do you do this - on a trip that usually last only a few days and usually has you shooting a critter towards the *end* of the trip?

Assume you've killed something not big enough to pay for taxidermy. Do you pay a taxidermist to professionally clean the skull plate? Have them ship it later? What constitutes 'clean'?

Boil the skull to remove the flesh/brain material?

Scrape it out the best you can and then spray it out at a car wash.

My neighbor has it down to a science, a 55 gallon steel drum filled with water and lye on top of a 'Turkey Fryer" burner.  Deer, Elk whatever she shoots and wants the head and antlers.

Hmmm.

A 3-gallon turkey fryer wouldn’t be burdensome to throw in the car before the hunt.

I suppose I could do a wire brush then boil in lye then bleach then brush again then dry it out.

On our out of state trip, or ones that are mounted, we have a local taxidermist that will cape the animal and cut the antler plates off.
For non mounted, we clead as best we can.  Stick a screwdriver up in the brain cavitiy and flush as much as possible.  Or we cut the antler plate off and mount in a store bought skull mount.

Become ungovernable

https://www.raptorazor.com/products/deer-scrambler

I used one of these this year, basically a drill bit with weed wacker string strung through pre drilled holes.

Worked well. Stuck the elk skull in a stream and went to town. Took all of about 5 minutes.

The harder part was caping out the skull.

We just had a local do it and ship it to us.  It cost us $140 for the euro mount and another 50 to box it up and ship to us.