How to record self reported sales tax on purchases of second hand equipment

Hi -

I'm required to self-report provincial sales taxes (PST) on purchases of second hand equipment when the seller does not collect it.

I have created a supplier called "Second Hand Purchases".

Let's say I purchase an item for $100, and enter that as an expense (or bill) to the "Second Hand Purchases" supplier, with an "out of scope" value for the tax. This expense (total $100) will match with the cash withdrawal or electronic transfer from my bank account.

I also need to add $7 to a PST liability account; my preference would be the PST liability account that QBO created and uses to record the PST included in regular purchases where the seller charges this PST.

If I set the tax rate in the expense to the PST rate, it won't match the bank transaction amount.

I've tried adding a journal entry crediting the $7 to the PST liability account, but that requires an account to "debit"- but this is a liability that has yet to be paid!

I think I tried adding a bill to the PST liability account, but that wasn't allowed.

So how do I record this liability correctly so my year end reporting of what's owed is correct?

Thanks in advance!