hey there
Ive just bought the same tank as the ones Graham Goode stocks..and the tank has the swirl pot inside...which should mean that it does not suffer from the surging the older aftermarked tanks did.They came without the swirl pot/or baffle pot inside.the one i got..and the one from Graham Goode will come with one.That said..i dont know 100% on GG "s one will..BUT ..one thing is certain..my aftermarked tank has the swirl/baffle pot inside..AND the GG tank does have the same manufacturer stamp on the outside..so i reckon 99.99% it is the same tank.So you should be all good .Cheers from Norway,Stefan