I haven't done it.
No, you're not nuts.
I don't sling Evan all day long. I don't think slinging is necessary to EC.
Just do what you can to catch the pees and poops of whichever baby. Whatever you can do is great, no need to achieve perfection.
If you catch a pee in the sink or toilet, you don't need to do anything (except rinse). If it's in the Baby Bjorn little potty (highly recommended), just dump it in the sink or toilet.
If you miss a pee, no biggie. Change the diaper, wipe the floor, change your shirt :LOL whatever!
We catch about 90 percent of the poops but who knows how many pees. We usually get the ones after he wakes up, but we don't get them all during the day.
Remember, the perfect is the enemy of the good!