Railcraft's Tanks and Modem's problem

I'm trying to get info of Railcraft's Tanks with

local tank = peripheral.wrap("rcsteeltankvalvetile_0")
local tableInfo = tank.getTanks("unknown")

It gives me error

test:2: attempt to call nil

Its connected via modems. All modems are connected. I found this code, but only with "sides" variant.
Thanks for your help

Already solved it, the "unknown" should be replaced with name of modem too