Hello,
I can only give you a house number that is circulating in the forums and which I can experimentally estimate to be

, and which I have used for troubleshooting (air) in the van by directing the return flow into an empty bottle). Afterwards, at the rated speed, approximately 1 liter per minute flows back into the tank, and with full load, correspondingly less. Therefore, the forward flow volume is in this order of magnitude.
The impeller pump of the 1Z is likely identical or very similar, so transferring the specifications seems permissible in my opinion.
Best regards, Uli.