Little E is right, I use the Coloplast Assura Extended Wear wafer with an Eakin Seal underneath and easily get 7 days wear from it. It's a two piece system, so you can snap on different size pouches. They carry a mini that I love for swimming and intimate times. It's so nice and small.
The wafer has a built in skin barrier, so I do not have to use any skin prep. I've tried it, though, just out of curiosity, but the wafer would not stick to my skin, so I gave up on it.
This wafer is so waterproof that I can swim in the pool all day, and still get a week's wear time!
I highly recommend adhesive remover wipes. They make the wafer slide right off.
Dx'd Crohn's in '99 at 28. Proctocolectomy and ileostomy in '06.
Disease-free, medicine-free, and very thankful to be healthy again :)