This pump does not have an anti-siphon valve or a one-way valve, so fuel can flow in either direction when the pump is off. https://www.pegasusautoracing.com/productdetails.asp?RecID=83

Rotax recommends/requires a bypass check valve around the electric fuel pump so that in the event the electric fuel pump fails or is turned off, fuel can still flow around the pump and feed the engine. 

Please see Chapter: 73–00–00 ENGINE – FUEL AND CONTROL in the Rotax installation manual for more information - https://www.rotax-owner.com/pdf/IM_912_Series_Ed3_R0.pdf

Thank you for the information.   I think I misunderstood the person I was talking with in regard to the one-way (bypass) check valve.  I have read the Fuel and Control in the installation manual and needed clarity on the check valve.  

Thanks also for the link to Pegasus.  I have not used this supplier.