Gunge in brand new tank?

Evening all. After cleaning my tank out, re-fitting it and filling with diesel, it started leaking

My replacement tank has arrived today but has what looks like brown slime in the bottom of it.

It's brand new so not at all what I would expect.

Is there something I don't know about new tanks or should I be contacting the seller?

Cheers

Tez

Sounds like it's been stored outside?

it's not britpart is it?

No, not britpart. I've been in contact with the supplier and they have been great. Very apologetic and sending a replacement tomorrow.
Only asked as I've never had to fit a new tank before. I've never had a 28 year old car before either:crazy_driver:

AAAARRRRRGGGGGGHHHHHHH. The new bloody tank is half an inch wider than the old one. The old one scrubbed the sill and the chassis not way out so there is no way this new "extra wide but identical to OE" tank is going back in. Think il just cut the floor out and go all Fred Flintstone.