Jeeze you musta had some gnarly klingons on your rear end if you had to use a wire brush/sandpaper...and a power washer to get it clean!!!
I had a leaky main seal for about 6 months haha The entire undercarriage was NASTY, buuut I cleaned up everything with a couple of wire brushes haha! I wish I had some pictures of that day and a half... I looked like I'd jumped in a puddle of tar! Haha.. Yeah when a normal (I don't know how to spell the name of those toilets that spray water on your butt, and I'm not gonna try) isn't powerful enough, go to a local car wash and ask to use the good 'ol pressure washer. I could also go the Tijuana route and get some giant zip strips and hold it on that way