Lookup (relationship) from Multiselect field to Table

Wow.. even the subject sounds confusing.  haha.

Here is what I'm trying to accomplish.

I have a contact list (table) and in that table I added a multi-select field for "marketing lists".  The values for this field are populated from another table called "marketing tags".  

When I add a new record to the "marketing tags" table, I use pipelines to create a new "tag" in MailChimp.  Once the tag is created in MailChimp, I get the "tag" ID and enter it into the "marketing tags" table in a field called "TagID". (FYI, i couldn't find a way to retrieve the tag id from mailchimp via api (webhook), so I just do that part manually).

So, the end goal of this is that when you view a contact, you can select multiple marketing lists for them to be assigned to in MailChimp.  So, if you select "business" from the multi-select field, it would assign the "business" tag to that contact in MailChimp.

Where I'm having issues is looking up the "TagID" associated with "business"  from the "marketing tags" table (via relationship?), so that it can be used when building the pipeline to assign that tag to the contact. 

Hope I this makes sense, and I understand how this works with single data fields.  but when I have multiple tags for one contact, how do I lookup multiple "TagID" ...

Thanks

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Mark Corcoran
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