Buttwoman and pmoi, I think I can solve your issues of animal plugs being too small and tails not being removable for cleaning. It's kind of pricey though.
First, buy the animal tail you want, and remove as much of the tail as you can from its little plug.
Second, buy one of these 3-inch plugs/enema nozzles with a 1/4" bore hole (or similiar 2.5" or 2.0" plugs from the same site):
OR this 3-inch beauty with 10.5 inches of insertable length, (which I've got an order in for now):
Third, cut a short length of wooden dowel of a greater than 1/4" diameter that stays put when you jam it into the silicone plug's quarter inch bore hole. Then attach the animal tail to the dowel. There should be lots of options for doing this very securely.
Finally jam the dowel with tail attached into the 1/4" bore hole, and then enjoy jamming the whole assembly into your butt, (or whoever's butt needs a tail.)
You could build up a big 'wardrobe' of interchangeable animal tails attached to dowels, and you could start making your own weird tails, like a slinky with a rubber ball on the end, or weird butt decorations like a bouquet of flowers, a big red Christmas bow, a big gold star, glow-stick starbursts, or flashing red LED 'tail lights', (normally for bicycles.) My imagination runs wild. I want to go browsing in stores now to get some better ideas.
I bet if you did this right it would be a challenge to grab you by the tail and pull it out, but I'd like to try.