But if it's so easy, what's the easy process? i.e. is it even legal (assuming you have permission)?
And if it's legal, then how would you go about withdrawing the money given just the relevant information (account/routing numbers, name of the account owner, etc.)?
For what it's worth:
I would assume that forging a check using the account information to include is illegal, so I'm obviously not asking how to forge checks (or for any other illegal advice); I'm only asking how to go about legally withdrawing money (assuming you have permission or whatever else is necessary at minimum)
If it's only legal for an account owned by myself, then I would like to know how I would go about doing this for my own account (i.e., if there's a legal way to do it assuming I have relevant authorization -- either because I'm the owner or the owner has given me permission -- then I'm looking for an explanation of how this is done, not just an answer saying "it's possible")
I can't find any option on my banks' websites' that lets me withdraw money from someone else's account, so this doesn't seem to be supported? (yes I know this sounds silly, my point is that it doesn't look anything close to easy to me)
Websites like this say this can be done with the account number, but not how
I don't find any option on ATMs saying "please enter the account number of the third-party account you'd like to withdraw from", for obvious reasons
But I just can't think of any other way to make this work. Does a bank do this for me if I go in person? Or by phone? Or is there an obscure option on their websites for doing this?
You can technically initiate an ACH transaction (debit or credit) with just the routing number and the account number. As a consumer - most banks will not allow you doing this without some sort of verification of authority. But if you have a direct ACH access (like many billers do) - you can do that and nothing will stop you.
You can also print checks with the account/routing info on them and use them.
That said - these actions are illegal and reversible. People who do this are usually making "sting" operations where they deposit forged checks and withdraw the money in cash quickly, before the check bounces back as a fake. The loss is then on the bank that allowed them depositing the checks (that's why new accounts usually have much longer holds on deposits than older established ones).
A large biller is registered and can initiate an ACH Debit to your account based on the Account Number and the Routing number. He assumes responsibility and completes the due diligence of obtaining a written mandate / permission / authorization from you.
There are other legal process where by you get a Power of Attorney that would allow you to transact on behalf of someone.
The key point you seem to be missing is that one can ONLY transact from ones account either by walking into the Bank / ATM, or by writing a check. There are other options as well to transact.