OK so if you have some frozen you are looking at 16 oz. Plus you do want a bit set aside for emergency (dropped bottle, travel problems so add maybe another 3 - 5oz for that.)
18-21oz
That's quite a lot in only 3.5 days
.
How much do you have in the freezer? Is there any way you can reduce that?
I think the trick here is going to be little and often rather than massive big pumping sessions that completely mess up the subsequent feeds and leave you with major engorgement issues on the day you are away.
Does he feed one-sided or two-sided? That's quite important. If he's one-sided you could pump during a feed on the other side.
If not I would try and pump perhaps 30 minutes after every feed but only expect 1-2oz at a time and don't go on forever. The morning would probably be your best time when you could also get a little more.
You could also consider pumping once in the night.
You may find that your supply takes some adjusting afterwards but there's no real way to avoid that. You will also need to pump while you are away if you can - at least once or twice. If you really can't just expect an adjustment period on your return.
Good Luck.
