I use the bathtub, but my back is fine

But my mom who has a bad back, when she bathes them, she uses the kitchen sink(for the smaller 2), she doesn't bath Jasper.

Things that are also good are those ummmm laundry tubs?? Or something that my cousins use for their collie, not sure what theyre called, like big square sinks, and its up high so they don't have to stoop down