Kerry,
The tank needs to come out.

I guess its unlikely that you could get another tank being a TD.

With the sample you have, experiment to make sure its soluble in water & if it is soluble, water will do the trick. By experimentation on your sample of the s##t, you can see what will happen if a substance is used. unleaded gas is worth a try on the sample first.
If water mixes with the s##T, try inverting the tank & filling with water through the filler, you may be able to get all the s##t to come out the fuel line.
Air pressure does not appear to be your friend, water pressure may work better.
If you know any one with a boiler in a factory, you could steam the tank for a day. We do that on tanks to remove fuel before welding. It has the extra positive of heating the tank so if drained, it dries right out. If not, very hot water may be a substitute.

The tank will eventually be good, the IP is more of a worry. Best drain & flush a few times, not with water. The hard lines & injectors should ideally be removed & cleaned. Did the diesel purge mix with the s##t?
Does your neighbor know what the s##t is?
I guess at the moment you are between a rock & a hard place!!
Be very methodical in what you do, no knee jerk stuff, logical planned steps will get you on top of the problem.

__________________
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