managing stock for variable product

Just so i understand … You have a variable product with

Variation 1 = Single Bottle
Variation 2 = 6 Pack

If somebody buys a single bottle the stock is being altered as per a single bottle or multiples of 1 ?

But if somebody buys a 6 Pack you would like it to remove 6 bottles from stock ?

The problem is that the stock level for Variation 1 is relative to single bottles but a 6 pack is a single product of it’s own with no connection to the single bottle stock quantities.

If you set a stock level of 30 to Variation 1 then that equates to 30 bottles.

But for Variation 2 you would need to set the Stock level to 5 to equal 30 bottles.

Make sense ?

Now an easier way to achieve what you want is to create only 1 product for a single bottle, with what ever stock level you wish, then apply a discount for multiple buys, this will achieve the same deal for your customer and also manage your stock correctly for you.

This plugin can help you https://en-gb.wordpress.org/plugins/woocommerce-bulk-discount/

Now if i have misunderstood you then please ignore