How do you create the relationship back to a Parent table record from ""Orphan"" child records

One approach in these situations is to make a Sync table called parking Lot Sync in the same app to mirror the Parking lots table and then change the key field of that table to the Lot# as I assume it is Unique.

Then you can relate the catch basins to that Parking Lot Sync table.  That may be enough to solve your issue, but if you really do need to have them attached by a Relationship, then you can make a relationship between Parking Lot Sync to many Parking lots and then do a summary maximum of the [Record ID#] field can call it [Record ID# of parking lot].

Then look that up down to Catch basis and use that for your relation to Parking Lots.

Hmmm....that sounds like a huge undertaking but I do need to have that relationship.  Since both tables have the Parking Lot Number isn't there a way I can maybe place in the Parking Lot table a formula field that says if the record has Parking Lot Number 1234 then [Record ID#]? Then someway in the Catch Basin table have the same Parking Lot Number 123 translate to that [Record ID#] and use it to relate the records?  Hope that makes sense.  I'm having a lot of trouble with relationships in this huge application and have placed a number of postings with no good results yet.  This one is only one of the recent issues but also one the simpler.  

The other problems involve multi level relationships where I need to relate records back up about 3 to 4 generations. But that is for another day.

I don't see another way.  I can help you set this up if you want one on one assistance, but like you said you have hundred of records to link up and they will be changing in the future so you need something automatic.

Yep. Thanks anyway.