Terrific advice from everyone here. My dad is a crazy high transporter; his peritoneal membrane runs the sugar/toxin exchanges very fast. So any dwell lasting longer than 40-60 mins means he'll be reabsorbing fluid. He does have residual kidney function, so I'm hoping that he does indeed pass out some of the fluid when he goes to the restroom during the day. I haven't asked our nurses about extraneal (non-absorbing) fluid; that might be an interesting option for long, manual dwells.
Because my dad uses a cycler throughout the night (Liberty), we can control his dwells, but with dwell periods of only 40 mins, it means at least 9-10 exchanges in a 9 hr period. And he also wakes up during every fill/drain, and so he never gets a full night of sleep. As a result, he's incredibly moody and sleepy throughout the day.
So as someone suggested earlier, you might want to find out what type of membrane you have, and how long you can dwell before you start reabsorbing the dialysate fluid. If you're doing manual dwells, it's pretty easy to figure this out. Record the UF returns you get with different dwell periods. You should notice that with longer dwells, the UFs will decrease. You should always, ALWAYS first consult and work with your NURSES to figure out the best way to find out how long a dwell is TOO long...