Hi petersaxon28,
Welcome to QBCommunity!
You can store a supplier's BSB number by selecting Edit from the Suppliers page, and ticking the box I create batch payments to pay this supplier, and then selecting Save.
Here is also a handy article on how you can use stored Supplier bank accounts to create batch payments to your suppliers: https://quickbooks.intuit.com/learn-support/en-us/manage-suppliers-and-expenses/how-to-enable-batch-...
Bonny