[Solved]Making Forge mod blocks compatible with vanilla Hoppers

So I have some blocks you could call custom furnaces. They have only 2 slots: one input, one output. Input is slot 0 in the container class, Output is slot 1 in the container class. I changed this in my TileEntity class to adjust for it only having 2 slots (code is based on original BlockFurnace code):

private static final int[] slotsTop = new int[] {0};
    private static final int[] slotsBottom = new int[] {1};
    private static final int[] slotsSides = new int[] {0};

So now I can place items in the input slot (slot 0) through hoppers via the top or sides of the block and it works correctly. However, I can't output from slot 1 through the bottom. Items stay in the furnace without moving. Any ideas how I could rectify this?

Edit: Me, being completely blind, managed to miss this method:

public boolean canExtractItem(int par1, ItemStack par2ItemStack, int par3)
    {
        return par3 == 0 || par1 != 1 || par2ItemStack.getItem() == Items.bucket;
    }

Being from the Furnace TileEntity class, it by default disabled slot 1 (represented by int par1) from being withdrawn from. Changing it to:

public boolean canExtractItem(int par1, ItemStack par2ItemStack, int par3)
    {
        return  par1 != 0 || par2ItemStack.getItem() == Items.bucket;
    }

Has made it so items can be withdrawn from my blocks.