Just dump the fuel out. Swish the last bit of gas around and dump it out. It should come out. You can use water and just swish it around and dump it out a couple times to get the chunks out, as long as you dry it and fill it up with fuel right away, before it starts to flash rust. Or just empty it and shake the pieces out
If there's big chunks, they won't get passed the petcock anyway, and your fuel filter will catch tiny chunks.