I make Jazzie stand on the toilet seat lid.
NOTE: It's imperative that the lid is in the down position or you will have a very wet yorkie.
Have some TP Torn and on Stand-by for UHO's* you may encounter.
Put a towel over the lid so they don't slip
Lift the tail firmly
Turn on the clipper
Trim a little at a time until you think you got enough
Croon "Good Girl" or "Good Boy" or "Good (insert name here)" in a reassuring way.
Don't worry, you may be a rookie but your kiddo is a Pro with sanitation trim by the groomer, so this should not be too foreign to him.
If you are asking "Why the toilet?", well if there are any UHO's* in the vicinity, the means of disposal is an arms reach away!
*UHO = Unsanitary Hanging Objects |