just went to the Deezee website and lifted this from their Auxiliary tank fuel connection kit. Looking at it is looks like the shut off valve goes where the drain goes. Same chance of leak as a drain plug. Since the gravity feed is not supposed to be used while vehicle is in operation I would think most safety concerns would be satisfied.
https://www.deezee.com/product/auxil...onnection-kit/
Shut-off Valve to Start and Stop Diesel Fuel Transfer
Flow Valve Must be Closed During Vehicle Operation
Gravity System Not Intended for Continuous Fuel Transfer
Only For Use With Transfer Tanks Meeting Federal DOT Requirements
Disclaimer-- no connection with any fuel tank manufacturer or re-seller.
Just interested in this thread
Please correct me if I am wrong