Lua Tank Control

local tank = peripheral.wrap("back")

local cap                -- Tank capacity
local amount             -- Amount liquid in tank
local percentfull        -- Percent liquid in tank

function getTank(tankPeriph)
    local tableInfo = tankPeriph.getTankInfo("unknown") -- Local to the getTank function.

    fluidRaw = nil
    fluidName = nil
    fluidAmount = nil
    fluidCapacity = nil

    for k,v in pairs(tableInfo) do
      fluidCapacity = v.capacity

      if v.contents then
        for i,w in pairs(v.contents) do
          if i == "rawName" then
            fluidRaw = w
          elseif i == "amount" then
            fluidAmount = w
          elseif i == "name" then
            fluidName = w
          end
        end
      end
    end

    return fluidRaw, fluidName, fluidAmount, fluidCapacity -- Returning the values of global variables (which are nil).
end

while true do

local fluidRaw, fluidName, fluidAmount, fluidCapacity = getTank(tank)

if fluidName then
    -- Get values for tank capacity and amount
    fluidName = string.gsub(fluidName, "^%l", string.upper)
    cap = fluidCapacity / 1000
    amount = fluidAmount
end

if amount == nil then
      amount = 0
      percentfull = 0
    else
      -- Use math.floor to convert to integers
      amount = math.floor(amount / 1000)
      percentfull = math.floor(100 * amount / cap)
end

if percentfull < 40 then
    redstone.setOutput("bottom", true)
end

if percentfull > 60 then
    redstone.setOutput("bottom", false)
end

sleep(2)

end