Nothing can remove the creative portable tanks, in singleplayer i found 3 wrenches that worked: Crescent Hammer, Multiblock fluid tank wrench, flux-infused Omniwrench
but neither of those work on the server, block breakers dont work either
Are the tanks in a claim? Does this issue happen outside of a claim? This sounds like a permission issue, but it might not be.
john01dav cant remove them anywhere