Plumbing is a sexual act involving a man and a female. The aforementioned male pops his penis in the girl's vagina, lubricating her ring, tickling and widening the said orifice. When that there hole is at maximum size, the man pops the scrotum and both balls in that bottomless pit of love.
That girl last night was a bucket, I was plumbing her without even realising. It was mint.