SQL Query - concatenate multiple fields into 1

Hello experts,

Not sure how to go about doing this.  I have about 5 left outer join to various databases with similar fields.  Now I need to join these 5 fields into one.  I tried doing the following, but if 1 is blank, then none show up.

(DB1.ID + '' + DB2.ID + '' + DB3.ID + '' + DB4.ID + '' DB5.ID) AS COMBINE_IDS

Here's my query:

SELECT	IM.ITEM_ID, IM.ITEM_DESCRIPTION, IM.MFG_ID
			
		(MFG1.MFG_ID + '/' + MFG2.MFG_ID + '/' + MFG3.MFG_ID + '/' + MFG4.MFG_ID + '/' + MFG5.MFG_ID) AS DB_MFG
			
FROM	ITEM_MASTER IM
		
		LEFT OUTER JOIN
		(SELECT I1.ITEM_ID, I1.MFG_ID
		FROM [SRV1].DB1.DBO.ITEM_MASTER I1
		) MFG1 ON MFG1.ITEM_ID = IM.ITEM_ID
		
		LEFT OUTER JOIN
		(SELECT I2.ITEM_ID, I2.MFG_ID
		FROM [SRV2].DB2.DBO.ITEM_MASTER I2
		) MFG2 ON MFG2.ITEM_ID = IM.ITEM_ID

		LEFT OUTER JOIN
		(SELECT I3.ITEM_ID, I3.MFG_ID
		FROM [SRV3].DB3.DBO.ITEM_MASTER I3
		) MFG3 ON MFG3.ITEM_ID = IM.ITEM_ID

		LEFT OUTER JOIN
		(SELECT I4.ITEM_ID, I4.MFG_ID
		FROM [SRV4].DB4.DBO.ITEM_MASTER I4
		) MFG4 ON MFG4.ITEM_ID = IM.ITEM_ID

		LEFT OUTER JOIN
		(SELECT I5.ITEM_ID, I5.MFG_ID
		FROM [SRV5].DB5.DBO.ITEM_MASTER I5
		) MFG5 ON MFG5.ITEM_ID = IM.ITEM_ID

WHERE	IM.MFG_ID IS NOT NULL

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