May one rinse tomatoes, grapes etc. in their plastic “baskets” on Shabbos?
One can rinse fruits in their plastic containers. These containers have holes and therefore there’s no problem with borer at all.
If there are no holes it is still permitted to immerse the fruits before eating them since the rinsing is just for an extra hygiene but not necessarily to remove any dirt.
עיין או״ח סימן שיט ס״ח ובשוע״ר סעיף יא. וע״ע בקצוה״ש קכה סקט”ז. שבת כהלכה פרק יד סעיף כב.