I was thinking something similar to LBJ – if you could line the cushion with something soft, yet disposable, you could maybe just toss the cloth when it gets icky or when he gets up to eat. Maybe cut pieces of fleece or a bed sheet? I know paper towels would be too rough on his little bum.
When I have had to do butt baths in the past, I did them in the bathroom sink. It was a good size for the bun (their butt lined up well with the faucet) and I put a wash cloth or hand towel in the sink and also on the side of the sink. It worked well for me because I could prop my elbow on the edge of the sink and support the bun, while using the other hand to wash with and the water just did its own thing. I could also set all the stuff within reach on the side of the sink.
I think letting the clumps soak in warm water for a few seconds helps in breaking them up. Also, for stubborn ones, rubbing them gently between your fingers with a wash cloth can help, too (as long as you don’t rub directly on their skin). Dawn dishsoap (the kind with no anti-bacterial stuff in it) is safe for washing, just be sure to get it fully rinsed. <!–/data/user/0/com.samsung.android.app.notes/files/clipdata/clipdata_bodytext_250403_111016_347.sdocx–>