You were lucky John !!
I like the idea of a piece of mesh in the fill pipe so that he cant get the sample tube in.
what would he do then?
Would have been good to ask him what happens if some one is running a waste ATF blend.
Sounds like you need a 2 tank system so you can put your off road diesel in the second tank !!

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving