The first apparent accurate reply was way back in #3.
from:
https://www.gpo.gov/fdsys/pkg/CFR-2015-title40-vol25/pdf/CFR-2015-title40-vol25-chapI-subchapH.pdf
you will read this:
(1) No person shall transport from
the United States any material for the
purpose of dumping it into ocean
waters;
(2) In the case of a vessel or aircraft
registered in the United States or flying
the United States flag or in the
case of a United States department,
agency, or instrumentality, no person
shall transport from any location any
material for the purpose of dumping it
into ocean waters; and
(3) No person shall dump any material
transported from a location outside
the United States:
(i) Into the territorial sea of the
United States; or
(ii) Into a zone contiguous to the territorial
sea of the United States, extending
to a line twelve nautical miles
seaward from the base line from which
the breadth of the territorial sea is
measured, to the extent that it may affect
the territorial sea or the territory
of the United States.
THere are almost 200 pages of this stuff; but metal beyond 12nm seems to be legal, just don't say it contains "sewage sludge" since that is specifically called out as special. I forgot where, in there somewhere.... I (we) have a lot of investment in this tank.