how to update Android via OTA when Multirom and TWRP are installed

Hi,
today I received a security update in my Nexus 5. I accepted it and when rebooted it got stuck in the multirom menu and it didnt update anything. Last time I have to lock the device and flash the rooted image in order to proceed with the update. this time I would like to do it diferently if possible.

Is there any other way to flash the update without removing multirom and locking back the device?
where is the update.zip stored when the system automatically downloads the update? maybe I could manually flash it using the TWRP.

thanks!
Jose