Your geometry won’t work here…

In a roundabout way

Well I guess they’ve got you over a barrel

They seem to be confusing feces with facets.

Defecating when the tank is rolling towards you, however, is perfectly understandable.

We don’t want your length around here!

Sounds like constipation.

When a Tank rolls over you, your bodily functions are probably beyond your control.

Euclidian mathematics is not approved by the Party,

Coprophobia is encouraged.

I can understand the problem.
When you have a populations of around 1.4 billion, it would take only 0.005% of the people to produce a veritable mountain of excrement.

Maybe the prohibition is directed at any arsehole that can pump out a stump of equal dimensions to the cylinder.

Defecating around or inside the TARDIS?

Epic oxymoron.
The signpost itself is a 3-dimensional object.