Multiple databtables, add data row is not co-operating

Maybe it is more easy to use “filter datatable” and “merge datatable” instead of add…
first you filter the desired row from dt3 to dt_temp (check Keep)
second you filter the same row from dt3 to dt3 and (check remove)
now you do your mail-Thing and what-ever with dt_temp
after that, you merge dt_temp to dt2
and now you filter again dt_temp (check remove) and the datatable should be empty (or use clear datatable)

But if you add the datarows to dt2 you will have probably the same datarows in dt2 as right from the start - or not? (by merging dt2 to dt1 at the beginning)