Hi there, welcome
My boy Bunston HATED being picked up and restrained. I’m right handed, so I’ll describe the method that worked for us (for nail trims etc, so would work for cleaning his bum) with that handed-ness. If you’re left handed just flip everything.
I would start off by petting him on the head (with his head facing towards me) with my left hand until he relaxed a bit. Then in one swoop, I would slide my left forearm along side his body, my right hand would form a “C” shape under his arm pits (so thumb on shoulders, fingers supporting weight of front en), as my left hand scooped under his bum.
So you end up with the body pinned against your forearm, and weight supported by both arms, but legs not able to push off of you. I would then immediately tuck him against my body, with his head basically under my left arm. The more secure they feel the better, so be firm and deliberate. If they feel you loosen they worry they will fall and start struggling.
This really only works if you can get him on the first try. So if he squirms away, wait a while to try again.
Once you’ve got him, I would have him basically sideways on my lap, and would lift his front end up with my right hand hold him against my chest. I would then use my left hand to hold his bum up, as before. This should allow your helper to access his bum. I would always wear a thick sweatshirt because usually when we would finish he would turn and dig at me for a bit to show how angry he was, lol. But he would forgive pretty quickly
Does that make sense? i can try to make a video or take some photos if it’s not clear. I think the most important thing is to be firm, supportive, and confident. Once you get him on your lap you can also place your hand over his eyes to calm him down.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.