As you will quickly find out, cleaning Razor Clams is an art. The basic steps are:
Remove the clam from its shell by placing the clam in boiling water until the shell pops and then immediately submerging it in ice water.
Using a knife and kitchen scissors remove all the sand and brown stuff. You will need to explore a bit to find all the hidden places where this accumulates, like in the neck, digger, insides, etc.
Once complete, then look one more time for sand, grit, more hidden brown stuff, because nobody enjoys biting into a bunch of sand.
A experienced cleaner can clean 12-15 clams per hour. You do the math when digging the clams. If you dig 100 clams you probably have 5-6 hours of cleaning ahead of you.