yeah the large bummi's bags are tops - we used one as our wetbag when we were travelling for a month earlier this year and we could fit probably 3 days worth of nappies in there. Just use some pail pals or something if you are worried about the smell. We just put the wetbag inside our luggage and it was fine
if the hotel has it's own pre-paid laundry, just take enough powder in a ziplock bag or something if you really want to wash, but if you are only going for a few days, just enjoy the holiday and worry about the washing when you get back