Yeah, just link your local account to Marcus. Initiate the transfer from Marcus and they'll pull the funds from your bank.

Marcus has a very high ACH transfer limit ($125K/day push and $125K/day pull and you can call to get that increased), so moving $40K in a single transaction should be fine and is perfectly legal. My only caveat in general is make sure you don't need that money right away. With some banks, they may put a hold on the money for a period of time (may be up to 10 days or less) before you can then spend or move the money again. This is typical when you're a new account or are moving really large sums of money and this isn't specific to Marcus.

Thus if you need any of that $40K, it may be smart to keep a small portion at the old bank first and wait till the initial transfer clears before moving the funds over.