We have a commercial customer who has a checking account. They would like to sweep money back and forth between two accounts. We do not have an outside investment account for this purpose. We have the usual savings, mmda, now, cd within our bank. Is there a way to accommodate this customer? We were thinking Saving and checking. Also where would I find information on this (sweeps), I was looking in 12 CFR 329, but it isn't giving me the info I need.

The problem with setting up a sweep involving a savings or MM account is that transfers FROM that account are limited under Regulation D. Your customer would need to move funds from the Savings or MM account in person in order to get around those limits. And "in person" doesn't include anything except physical presence at a branch (or ATM), by courier or other agent, or by snail mail.

That is the hurdle we are coming up against. Is it correct that true sweeps involve an investment account outside of the bank?

That is the typical way this is handle to avoid the transaction limitations. The down side is that the balances leave the bank's books.