Give yourself plenty of enema and wash out your ass before the dare, get your big 7 inch dildo ready on a chair, as well as plenty of time.
(if you feel like you need to warm up before doing your 7 inch, do some 'prep stretches' if need be)
After prep, set this
random timer for 5 minute to 2 hours;
You can do whatever you want during this time, read a book, chores, stretch that ass agape with that dildo, but when that the timer rings, you have to immediately go to the shower, get your ass in the air and catch as much water as you can for 5 minutes; if you have a detachable shower head or a tub faucet use that, hold it up to your ass or put your ass under it.
If you don't have either, uhhh.. pm me :/
Once the time is up, take a measuring cup and measure how much you collected. The average human anus can hold, comfortably, up to 2 liters (about 68 ounces), so for every ounce you
didn't collect, out of 2 liters, that's how many hours you have to go without cumming.