Hi Audrey,
First off, the most efficient way to receive bulk rent would be through Buildium's ePayment system, which will automatically update the tenants ledger, mark the money as deposited, add the money to your bank account, and update the tenant with a payment received email.
However we understand not every client chooses to use our ePayment system, and some tenants will always prefer mailing in checks. So the fastest way to enter in a stack of checks within Buildium would be to click on the Outstanding Balances page (which can be accessed quickly by clicking on the number of tenants link in the outstanding balance dashboard).

Once on this screen, you can choose to sort property by property, or simply scroll down the list checking the box for all checks in front of you.

Then scroll to the bottom and click the receive payments in full which will pop up a screen to add the check numbers.

Once you hit save, all the ledgers will be updated.
This is the fastest method when receiving payments in full, however some tenants dont always pay off their entire balance, so I recommend for those checks to click the Shortcuts icon and select "receive payment". Use the search box that pops up to find the tenant or unit, and you will be brought to the receive payment screen that you are familiar with in your old process. The big time saving trick here is when you are done filling out the screen, click Add Another Payment instead of save payment...this will allow you to quickly move on to the next check with out any additional clicks.

Hopefully this helps you drastically cut down the time you are spending on rent collection. Check out the images attached!