I give all my plecos fresh veg almost daily . Never bother blanching ucchini or anything except potato which I boil till it starts to soften. Rarely have any leftover veg to remove as most other fish will also nibble at the veg and snails finish off the restMine used to get it 3-4 times a week although I had a lot of plecos in one tank.
I never bothered blanching it though, quick rinse and in it went, taken out when eaten or after 24 hours, whichever happened first.